Why do Seasonal Events get stripped down each year and not added too?

[Sotaris]

I'd honestly empathise if they'd of not put all the old free content on the paid store and added new content paid at the same time - I'm disgusted in them.

edit: It's a shame I can't speak Japenese and could voice my disgust in person or atleast on the Japanese forum that's more likely to be seen.

I'd guess you're new? This has unfortnately happened for years and will not change.
It's a double edge sword. Either you keep the stuff exclusive and not accessable for new players or put it in the cash shop 1+ year later the event and people never has to feel FOMO.

Google Translate is a option i guess if you really want to vent your frustrations.