The problem is the number of scripted shows doesn't tell us much about the number of quality scripted shows, and quality is in the eye of the beholder. TV has continued to adapt over the years, and people have different preferences. There was:
1) The original "golden age" in the 1950s when TV was just starting up. Because there were only a small number of channels and because everything had to be of general interest, these were relatively high effort productions but were unable to take any real risks. It tended to be more "light entertainment" than anything serious.
2) The 60s-70s was the dawn of color and the beginning to diversify into some level of special interest. But the increase in volume meant production values were typically far below film.
3) The 80-90s was when cable started to seriously challenge broadcast and TV became a mature medium. A lot of TV was pretty vapid dreck. The insipid laugh tracks and tired gags. But there's still a lot of nostalgia for the sitcoms of that era. Nobody was yet trying for a cinematic experience in TV.
4) 00s-2010s was the beginning of "prestige" TV (in part as a reaction to cheaply produced "reality" TV). Cable and early streaming produced shows like the Sopranos (cable) and House of Cards/Breaking Bad (streaming) that had dramatic ambitions and production quality of feature film. That era isn't fully over, but the streaming wars have caused the sheer volume of prestige TV to hit its limits.
5) 2020s-present has been defined by the rise of youtubers and the streaming wars.
The general arc has been more and more segmentation in entertainment. Early TV entertainment had to appeal to the widest possible audience because there were only 2-3 choices of what to watch. Today, there's content for every conceivable niche and it's available at any time of day or night (no competition for timeslots anymore). This is great if you want content tailored to your specific interest, but it can make it hard to break through as something intended for a general audience. With AI, we could envision a world where media is created specifically for you individually and the number of "shows" becomes infinite.