The beauty of the current AI is that it works for all troops.
Making a "smarter" AI for existing troops, in the existing meta, would be some work but not tremendously difficult. The big problem is that every few weeks, as new troops and strategies come out, it would get out of date, and need updating. "Better AI" is a huge, ongoing potential resource drain.
Compared to the current solution, which just works with essentially no updates. That's some genius planning, right there!