They are speed running or doing games through 100% which most people cant be bothered to even attempt but are interested in watching, there also are people who played these games years and years ago that just enjoy watching the games and those that like to play along.
They aren't asking people to pay them to play they are asking people to donate and giving them reasons to donate through various methods, its not like they are forcing people to pay to watch if you don't feel what they are doing is a good enough reason than you don't have to.
Its just a shame they wont be doing another final fantasy marathon anytime soon
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Its funny though they aren't even asking for much, 50k may sound alot for 1 person but when they have 20000 people watching at one time thats $2.5 per person even donating $1 from everyone that has watched the stream so far would probably be enough.
Maybe that is too much for some people.