I think the lack of a live action Disney+ Spider-Man series comes down to a few factors...
One, if it's staring Tom Holland, the worry is that it would devalue the current film series. After all, will people be as eager to line up to buy tickets to the next film if they can get their Tom Holland Spidey fix through a Disney+ show?
Two, if it's staring someone else, the worry is that it would devalue the current film series by introducing a second concurrent live action Spider-Man and may confuse audience members.
Three, circling back to Tom Holland, he's probably too pricey for a tv or streaming budget these days.
Sony doesn't enter the picture. Disney can do whatever they want with Spider-Man on tv. Still, that doesn't mean there aren't other issues with the idea.
I thought the reason there hasn't been a proper live-action TV series for Batman since the Adam West show is because, unlike Superman (who is arguably on the same level as Batman and yet
has had proper TV shows of his own in addition to feature films), they actually can't make a new live-action Batman TV show due to overcomplicated rights issue entanglements:
That's possibly part of it, but the Bat Embargo has been a thing at WB going back to the early 2000s, at least.