To grab something I said elsewhere, Spider-Man having a bunch of Spider-people likely is very good for other products. You can get new market segments to more thoroughly emotionally engage with the already well-known and proven Spider-Man product line. You have lots of possible media spin-offs and lots of merchandise. But comic books can't sustain all of them so it's left scrambling to figure out what to do with them all. So yeah it's likely a case of both. Comics don't exist to tell stories, they exist to grow IPs to be used and the Spider-man crop is VERY bountiful so it becomes a cash crop.