The problem here of course is that circumventing the ad blocking is the most direct way Facebook can find value.
You can make a similar argument that the RIAA/MPAA going after piracy is a waste of time. Again, focus on delivering value to actual customers.
If Facebook spent more time on making a friendly ecosystem / community I would be more open to signing back up again. Instead, it seems they are hyper-focused on advertisements at the expense of everything else.
And advertisers are asking them to show what they are doing to combat adblocking. FB isn't doing this to target customers least likely to convert, they're doing it to check a box for their ad sales team.
Revenue is (simplistically) the product of impressions and value per impression. It’s not therefore immediately obvious that moves like this actually do increase revenue for them, especially over the long term since one potential side effect of doing this is giving more ammunition to the ‘delete Facebook’ crowd.
Facebook thinks otherwise. Between you and them, I suspect they are more likely to have some evidence or trials to support their position.
You can't make money off something without any value to people. People have to "want" the thing
If they turn all their posts into <canvas> then it'd kill any accessibility features and the ability to copy-paste text and such so I doubt they'd go that far.
Even then, a scraper could run OCR on the canvas image to get the text out of it.