tl;dr people are not inclined to pay for search, so Perplexity's hand was forced?
However, as many studies show in Youtube/Meta/GoogleSearch ad revenue per user, the subscription price needs to be really high to match the ad profits.
If you want to maximize the profits, you include ads.
I am already pretty pissed at them for pushing the election widget so hard - you could click on the X, but it would come back on every new search I opened.