Corporations expect average people to read and abide by a ten thousand line EULA, yet it's too much work for them to respect a trivially parseable text file.

If we did, bot authors would comply by just changing their User-Agent to something different that’s not expressly forbidden.

(Disallowing * isn’t usually an option since it makes you disappear from search engines).

Any such law would absolutely have to include a requirement that all bots use at least some common element in their User-Agent strings to identify themselves as bots.