That rips off the advertisers and/or leaves the poor poorer.
For any given ad supported service, one of two things must be true:
(1) the ad spend was more than or equal to the cost of the service for those users
(2) the ad spend was less than the cost of the service for those users
From fork (2), it follows that the service isn't sustainable anyway.
From fork (1), it follows that the buyers of the ad slots in turn only make a profit if those ads led to sales higher than the ad spend.
But for any given poor person, buying that which was advertised on the ad supported service necessarily means spending more than they would have on a non-ad-supported version of the same ad supported services.
For any given ad supported service, one of two things must be true:
(1) the ad spend was more than or equal to the cost of the service for those users
(2) the ad spend was less than the cost of the service for those users
From fork (2), it follows that the service isn't sustainable anyway.
From fork (1), it follows that the buyers of the ad slots in turn only make a profit if those ads led to sales higher than the ad spend.
But for any given poor person, buying that which was advertised on the ad supported service necessarily means spending more than they would have on a non-ad-supported version of the same ad supported services.