Even Tom came out on the Insider channel and said they wished YouTube could get rid of subscribers in general, and having that as a rule seems to be more detrimental than not. Just run with the watchtime requirement. It's the 'harder' of the two, and the sub requirement just causes more sub4sub. People think they'll subswap up to 1k and then make five videos that will get the watchtime requirement due to that audience size.
They won't admit it, but the only reason the 1k subs and 4k watch time was implemented, was in the hopes that "bad actors" (channels exploiting the system for ill or even illicit intent) couldn't be monetised. They hoped the "Bad actors" wouldn't be able to accumilate 1k subs and 4k watch time to be able to make videos that were against terms of service, and get paid for it, because the more far reaching implications, is if you YouTube pay everyone ad revenue, despite their subscriber count... they're essentially "paying" potentially very bad videos. And in some situations, can be seen as funding organisations using YouTube as a platform to promote illegal activity, and thus, funding crime. This was pointed out during the "elsa gate" and the first range of restrictions came through basically after that, and after pewdiepie did his naughty video, and advertisers started pulling their support of YouTube because they SAW their ads were being shown on these "elsa gate" videos and other questionable videos.
It's hard to get 1k subs, thus people can't get paid as easily for uploading just about anything regardless of it's content.
It has impacted a lot of innocent channels... BUT if you don't keep it, the 1% of bad actors can just make a channel in a few minutes, and start making ad revenue off any type of content that shouldn't be on YouTube. So Susan and the higher ups would never admit that was the purpose, but it's pretty obvious that was the reason.
The restrictions have even harsher after what happened with Logan Paul and the forest. They didn't outright say that was why, but youtube were playing the reaction and catch up game. Putting restrictions in to make it look like they were taking action against that kind of content being easily made and monetised in the future.
And the restrictions on mobile streaming (yes, you can use other streaming apps to stream to youtube mobile to bypass the 1k requirement for mobile streaming) but the NATIVE streaming method was restricted after what happened in NZ when someone livestreamed horrible events, because up until then, anyone could jump on mobile and livestream regardless of their subscriber count. It was the first time to ever happen (the guy even said "subscribe to pewdiepie") but that one time was enough to push YouTube to have to act so it looked like they were taking action, and as painful as it was for smaller channels, it was a good move overall, because if YT didn't take action, the government would have stood in, and then we'd have far more than 1ksubs and 4watch time to worry about... if the government stepped in, you'd see creators needing media licences in order to be legally allowed to distribue digital media on a platform with little to no government regulations.
So really, we got off increadibly lightly. But YouTube never mentioned these as the reasons, but it's not hard to see the timing all lining up.