Paying does not guarantee anything. It does not guarantee a more reliable service, it does not guarantee that they will hear you out when they change a feature or the design, ruining it, and it does not guarantee it won't shut down tomorrow. They will refund you, and you will have your money back, but you will have no service, and you will be back in square one.
I mean... sure. Even paid services eventually shut down.
But I have far more confidence in something at least making sense for the company to keep running if it is something I pay for vs something that is just given away for free.
If I am relying on an online service, while paying for it doesn't guarantee it being up it's a safer bet than a free one.
But that is likely part of why reader shut down. Depending on how often it's pulling and how often you are reading, that isn't free to run.
Especially if you don't even use their app to read your feeds, you may never be able to see an ad.
Would rather pay for it personally so I know it's there.