I'm seeing a lot of rose-tinted nostalgia glasses. Obviously your opinion of any given clip is going to be subjective, but objectively as time goes on video/audio quality increases, and a much greater number of people are producing tickling videos. There's just a whole lot more material out there now, making a wide array of different styles of video available; it seems really unlikely to me that just as tickling video production actually becomes an established thing everybody suddenly forgets how to make good videos for no particular reason. And personally, in 9/10 cases I prefer the newer videos to the older ones.
Characterizing it as "rose-tinted" is a misnomer. And if it really seems "unlikely" to you and you prefer the newer videos to the older ones, then I have to ask: have you even watched any of the older videos and what is your preferred style of tickling?
There was a lot of crap back in the old days. But most of my favorite videos of all time were from the prime of TP and RT. It's quite simple really; I don't know how they did it, but the girls were extremely ticklish and they kept coming back for more. Maybe the money was easy, they didn't take themselves too seriously and it the producer was fun to work with.