~snip~
Not possible. Just do some simple math, and you'll see.
I know this because I tried it several years ago. Clicking on one ad takes 3 seconds, on average.
50,000 x 3 = 150,000
150000 ÷ 3600 = 41.666666667
You need around 42 hours for clicking 50k ads, and a day has only 24. From my experience, not only $25 or $5, but even $3 per day is hard to achieve with this extremely exhausting activity.
You are forgetting that these people do not usually work at one place and not on different hours, you may think that 50k takes 42 hours a day but in reality that's like 5 different jobs at the same time so it takes only 8 hours a day, quite a compact 8 hours a day which you might say is not realistic but I can tell you that I am working 8 hours a day right now (not ptc) and it is quite compact as well so it is quite possible.
Ads could take as much as 15 seconds and it wouldn't matter because they are doing multiple at the same time and still make money. Hell some people literally open up second or third accounts on the same place with a multiple computers they get for cheap and do that there at the same time as well. I know they are not many in number but that is how that business works and there are few who does it.