The average woman on dating sites gets hundreds of messages, and the average guy gets tens. That is a MASSIVE imbalance in favor of women.
It’s not hard to imagine that this could cause problems that would lead to a group like incels being created.
I think we need to look more into the cause (why are men so devalued on dating sites) and not the symptom (why are men getting bitter and becoming incels).
Not sure that's necessarily a massive imbalance. It depends on the quality of the guy sending you those messages, and maybe on the actual message that they send (but it's more important that the guy is hot than that what he says is funny or something).
For example, I get a ton of emails from spammers about penis enlargement methods, and I rarely send my own emails asking if they have any penis enlargement methods available. Does that mean there's a massive imbalance in favor of me? It's not like I'm at a huge advantage because of all this email I'm getting.
Incels are due to gender skew being realized. Appearing larger than true, mainly due to marketing and lumping in with males who weren't getting any anyway (, are shy/insecure, and/or still in high school).
Men are generally lauded by society for casual dating and "spreading their seed," while women receive the opposite treatment. They are still generally honored for being very selective in their dating and only engaging in a monogamous relationship with the best mate. Hence, many men end up trying to sleep with most women on Tinder, while not committing to a monogamous relationship. While more women are trying to find the best mate that will commit to a monogamous relationship.
Note: The above only applies to hetero dynamics. I'm ill informed on lgbtq+.
Anecdotally I don't believe this to be the case anymore. A good quarter or so of the women I see on dating apps pretty proudly claim they're polyamorous.