For HTTPS you need a dedicated IP since security negotiation happens before the HTTP hosts header is posted and your cert needs to cover the host you want to connect to. That is, it is impossible to host several sites using HTTPS on one single IP. HTTPS using SSL (instead of for instance TLS) means that this is a limitation built into HTTPS itself and can't be mitigated.

With the current shortage on IPv4 IPs and most shared hosters trying to squeeze as many websites as possible onto the same single IP, that effectively means that getting a site up and running with HTTPS (and that is not even mentioning the cost of getting a properly signed certificate) is very, very costly and hard compared to regular HTTP hosting.

Until IPv6 goes mainstream don't expect any of this to change.