Two classes of technology startups are doing well these days, pulling down enormous valuations and aggregating top talent in Silicon Valley.

The first is applications that have strong self-reinforcing and highly scalable growth mechanisms. These are generally the messaging, photo and sticker-focused services that can at least theoretically reach more than a hundred million global users.

The second is services that monetize extremely well at the unit level, allowing them to buy growth while remaining profitable. These are the real world services and virtual games than can churn out meaningful revenue. You might think of Uber or Airbnb as well as certain gaming companies like Riot Games.

The bifurcation represents a new reality about growth. Once subsidized by channels like search, social networks and app stores, growth is getting more expensive as the marketplace for attention has become more competitive and the tools for allocating spend have become more sophisticated.

To grow today, you either need to be a growth-focused product and engineering organization (like you see in the best messaging and photo services) or be profitable enough in a scalable way to buy your way in to the market (real world services and games).

This leads to big challenges for companies that don’t fit squarely in either camp. These services can be valuable, well-crafted and loved by their customers. But they can’t scale fast enough or make enough money to buy growth through marketing, subsidies or other forms of customer acquisition.

A wide swath of applications fall into this camp: fitness trackers, journaling software, email clients, calendar apps, to-do lists, presentation software, maps, photo storage, music services and more. As a group, I short-hand them as “single-player tools” because most serve an individual use case.

In the past, this class could survive and even sometimes thrive thanks to an ecosystem of relatively inexpensive distribution. But in the new growth reality, they lack strong enough internal growth or strong enough unit economics to compete.

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Many great teams are still tilting at these services, motivated by the fact that most legacy software in these categories leaves much to be desired.

Many good companies in this category end up getting acquired in talent acquisitions by their higher growth or more profitable brethren before they have a meaningful impact or become real businesses. Apple buying productivity app Cue is one example, or Dropbox buying Mailbox.

Of course, less successful companies getting acquired is pretty common in and beyond tech. What is perhaps new, however, is how clear the trend is among certain apps struggling from the same new reality around growth.

This dynamic is also leading to a very lopsided customer experience. The social applications and highly profitable services I use are improving rapidly. But the single-player, individualized productivity tools I use generally languish, only sometimes supported by behemoths who acquire them with little meaningful pressure from startups to keep innovating. I am still waiting for a next-generation calendar app and a truly successful fitness tracker.

The new growth dynamic also plays a big role in the perception that Silicon Valley is working on frivolous or irrelevant things. While I don’t think this perception is true, I believe it exists, in part, because some mechanisms that drive high growth at high scale (very viral mechanisms like sending stickers or sending a “Yo” to someone) can seem basic or even trivial.

The optimist in me believes that some of these single-player applications may eventually find better business models that allow them to buy their growth at current market prices. If zero-marginal-cost consumer software could be more sustainably profitable for small companies, software would get better and consumers’ lives would improve.

Micropayments is another often-floated option. It is undeniable that the app-store model allowed a whole class of small developers to flourish, at least for a little while before the big boys came in and the market rationalized. But I am skeptical that charging small sums for these services or additional features could change the fundamentals of these businesses, in part because they haven’t so far.

Perhaps the lack of good software in these areas could be filled by non-venture backed, small “bespoke” developers who don’t need huge multiples and massive growth to provide their services.

I look at Paul Mayne of Day One, a journaling app, as an example of a developer who builds and maintains a great piece of software and a solid small business. Sadly, I don’t know how many Pauls there are out there. And even if there were many of him, I am not sure his model works for problems which require more multiplayer adoption (like calendaring) or more complexity (like maps). Those services generally require bigger teams, among other things.

The pessimist in me thinks I better not hold my breath waiting for better single-player software. The growth dynamic has shifted appreciably. And when passionate entrepreneurs ask me for advice about a startup idea that doesn’t throw off a lot of cash or have enormously powerful organic growth potential, I generally suggest they change course and pick an idea in either camp. Ideas in those camps aren’t guaranteed to mint billions. But they have a better shot.