Why do you think convenience stores, supermarkets and coffee shops in Japan introduce new food and drink items so often?

People like trying new things. Sometimes they become best sellers and stores make mulla bucks from them. (This is an obvious answer, of course.)

Isn't Japan popular for its seasonal and limited edition products ? It's kind of their thing.

People stop consuming a lot of things just because it is perceived that new must be better, so companies accommodate that by introducing new variations constantly, or by making insignificant changes and calling their products in a different way.

This is all corporate sellers, isn't it.

You're local independent ramen joint won't do it. You'll local kissaten coffee shop won't do it. If you have one, your local corner shop won't stock new biscuits or new flavours of potato chips anything like as frequently as Family Mart.

If you go exclusively to independent ramen joints or coffee shops, you will have something different in every store. However, McDonalds and Starbucks have proved that's not what folks want. What they want is consistency. The limited edition stuff will be mostly to break up the (probably inevitable) boredom.

Same reason why Apple, etc release a new iPhone every year.

Well you can buy Halloween Kit kats and even Halloween lettuce which are completely different to the regular ones as they have a pumpkin or bat on the wrapping. Then we have Xmas..

Because they want to make money

Probably as an attempt to excite some kind of interest in their boring products.

Do they ?

it’s just new packaging, slightly pimped versions of the same. Different names and size.

jt’s called marketing. Something Japanese are very bad at. Having a namecard saying “ marketing manager” does clearly not produce marketing skills.

if you mean version 354B of a kitkat bar is new, you are right

It's capitalism: give people apparent choice in the things that don't matter, and restrict their choice in the things that do.