The monthly subscriptions plans are an open theft of customers money because of variable number of days in a month.

It's basically free money for companies with monthly pricing strategy.

It’s calculated at a month being ~30.4 days on average for the period of 12 months.

Companies expect you the consumer to be onboard long term not on a month to month basis.

So your 31 day months cover the 28/29 day month and it all balances back out.

Otherwise... what you expected them to bill you every 24 hour period?

4 weeks plans are common today. So get one of these and you're paying for a constant time.
But you'd better calculate it to the end. Little hint: Check the number of weeks of a year.

This is a fun bit of logic, let’s reverse it, why are you ripping off companies by paying the same amount on months with 31 days you filthy freeloading peasant?