It's probably just a matter of prioritization for the developer(s). They may have thought that it is harder to write an AI than it is.
I wrote an AI, and getting it to intermediate level is pretty easy. It's using a greedy algorithm, which is neither computationally expensive nor hard to code up. Getting it to 'advanced' level, especially with certain scoring cards (Lost Barony, Shieldgate etc.), is probably pretty tricky.