I don't think wholesaling is dying out, but I think it depends on the deal in question. A lot of those who started out in wholesaling just have more capital to leverage in other investment tactics, where they may not have had in the beginning- so when they find a deal that may be more profitable to fix & flip, or rent out, they're more capable of taking this on, themselves, rather than outsourcing an end buyer.
I also feel like Creative Finance is gaining more traction, so more wholesalers are able to use this leverage to get more deals, rather than letting leads die, because they're not able to meet a seller's price.
If wholesaling WERE to die out to landlord & flipping, I'd say it's purely due to outreach. Wholesaling takes a lot more effort to reach out to leads, phone calls, follow-ups, & the works- whereas with the other, deals sometimes just come to you, or you can find deals on-market. A lot of people, when getting into wholesaling, just don't really realize how much time & effort needs to go into building the business up.. mainly because of how it's been glamorized on social media by all these "gurus" who make it look easy. Unless you have a TEAM behind you, able to make cold calls, do lead follow-up, buyer outreach, & everything else.. wholesaling takes a LOT of commitment, but is totally worth it.