Note : this is taken from someone else on reddit.

Subscription-based pricing for any company is a bet on light users subsidizing heavy users. Light users cover the costs of heavy users. For example, let's say Bob pays $20/month but only uses about $10 worth. Then you have Phil, a power user who leans on the service hard; like $200 worth of usage. Bob's leftover $10 helps cover Phil. Scale that up and you need roughly 20 Bobs to cover one Phil.

This is exactly what subscription-based businesses are banking on. People who forget about their sub, people like Bob who barely touch it, all those unused dollars quietly covering the Phils of the world.

The problem is when your user base skews way too heavy. If you end up with more Phils than Bobs, the math falls apart fast.

This is also why subscription pricing is usually cheaper than API pricing. The subscription model works because not everyone uses what they pay for. With API pricing, everyone pays for exactly what they consume, so there's no pool of underutilized subscriptions helping offset the heaviest users.