For the people who actually make the shows, the continuity became a chain that hindered their storytelling. Now whether it -should- have is open to debate, but there are always going to be people who think they could have written something better than what was presented.
Furthermore, it's a historical fact that tv shows until relatively recently weren't especially continuity heavy. TOS was almost entirely one-off episodes that could be watched in basically any order. TNG also had its share of one-offs. That may not be what you prefer, but please don't claim your preference is universal. Even today, when tv shows have generally become more continuity-conscience, there are exceptions, and there are people who prefer the exceptions.
Also, I don't think most tv series actually make it to 10 seasons.
It's ludicrous to criticize the films for only having two films of...well, anything really. You said it yourself, it's -two- films. Would you judge all of TNG based on the first two episodes?
It's galling to me that Trek fans, who theoretically value a show that embraces diversity and open-mindedness, can be so close-minded and judgmental when someone tries to do something new with the franchise.
Star Trek isn't The One Ring, and we should not behave as Gollum.