The reality is Sony has become known for really massive, expensive games. Their quality is usually considered amazing by those that play them. If Sony made a decent amount of AA or lower AAA games they would be pumping out more games than they do, but they don't.
Nintendo, on the other hand, makes a few massive, expensive games (like Botw, SMO, Xenoblade Chronicles 2), but the vast majority of their games are AA or A in terms of resources needed to develop, making them able to pump out a lot more games. Even comparing Nintendo's big hitter's budgets to something like Spider-Man, Ghost of Tsushima, or The Last of Us would probably show Sony spends a lot more money on those AAA games.
I bring this up because as hardware advances, Sony's fans expect them to make games that push their hardware, and so Sony is forced to primarily focus their resources on those kinds of games, reducing the overall quantity of games they can produce in the same time period as Nintendo. Nintendo, on the other hand, doesn't have those expectations set upon them by their fans. We are just as happy to have Animal Crossing, 2-D Donkey Kong/Mario games, Kirby, Advanced Wars, and a ton of other games that cost a lot less to develop than Botw/SMO/XC2. In fact, many of us are happier by those experiences than the big-budget games. I'm not blaming anyone or even saying this is a bad thing. I'm not sure which happened first, the chicken (Sony making primarily expensive games) or the egg (fans expecting primarily expensive games), but somewhere along the way, that expectation was established. They are doing very well financially, are selling a butt-ton of hardware each generation, and I think their fans are generally happy with this arrangement. This isn't a criticism, it's me brainstorming why this trend exists in response to anyone who seems disgruntled by their lack of quantity-based output. I'd imagine if polled, Sony fans would rather have 3-6 games a year with an average higher budget than 10 games a year with an average lower budget.