UP Evaporate doesn't seem to trigger "User was awarded points" event in Rules.

This is expected; the module was written to be able to handle simultaneous point evaporation for (tens of) thousands of users. To trigger rules, it would need to process this step individually for each user, which would in most cases mean a completely failure to run (cron would either get killed after it hit its max run time, or a cron run would take longer than the cron interval).

You could change the guts of the module in hook_cron and replace the two queries it runs with a userpoints_api() call for each user that needs to have points removed.