Did he do it for the sole purpose of eliminating the girl Ayaka Sajou?
Or maybe he was planning to take down Enkidu indirectly, by destroying either their Master or the land the Holy Grail was rooted on?
The answer was yes for both, but while they were correct answers, they weren’t THE correct answer.
Don’t try to fool yourself. I hate the Holy Grail War. I hate this ritual and the guys who killed Flat for it. Humans... Human cities... Honestly, I quite liked London... But I don’t care about this city. ... Flat, there’s one thing I never told you about. The reason why you summoned that serial killer. That Heroic Spirit... couldn’t possibly be brought out by a toy knife. It was because of me. Because I have the potential to be a serial killer for humanity... and I’m not anyone yet.
This inner monologue was just a fraction of a second in the real flow of time, done amidst the fluid movement of dropping this asteroid on Earth.
But it didn’t escape Enkidu’s Presence Detection.
The tactic of perfectly concealing its magical energy backfired. In this space Thia and Enkidu made so turbulent with magical energy, one neutral spot becomes too conspicuous to go unnoticed.

Fate/Strange Fake, Volume 7; Chapter 21 (Beings Shaped In Man's Image)