Why doesn't PS5 support 1440p when it can do 4k?

Hate to say it, but most likely the reason is "just because". I'm guessing they assume people will use 4k now and 8k a little later. Anyone not on those is using HD at the amazing 1920x1080. Phew! They sell TVs. Do their TVs commonly support those 1440 resolutions?

Related gripe about Sony: they lost my business when they scrubbed the dev kit for the ps vita. I wanted my own games on there. Even preordered a book. Then when I finally had time and some tutorials and discovered I needed a key but the key server had been taken offline. So Xbox it is and not so much Sony. I don't buy anything Sony now. Its been so long but I'm still salty about it.

In an interview a while ago, the Playstation management mentioned they dropped 1440p to prioritise support for TVs. I believe Ito had also said there was no technical limitations for adding 1440p.

Everything else is just speculation. It could be that Sony's detached from people's needs? Perhaps the 1440p market is small in Japan? It could be because Sony wants to sell more of their 4K TVs?

Considering how "old-school" Sony tends to be, I'd wager it's a bit of column A