Imagine that in 2024 I tried to sell you a web browser. One that maybe has a slightly cleaner UI or some fancy plugin system but ultimately is just a plain old browser. Maybe some very small percentage of people would pay for it, but most are entirely happy with the free and FOSS choices available since the core features of a browser are standard.
RSS by all means should be similar: just like ping, cat, sh, browsers, email clients, video players, etc. the core features are well defined and an open source project should be the default choice. If you want something fancy or proprietary then sure you should be free to pay for it. But I can’t imagine wanting to build a company that pays salaries around any of this.
There are situations where a person or a team of 2-3 can make a lifestyle business out of selling something that I have seen referred to as “legacy software” (this doesn’t mean old, but rather fundamental and “boring”, aka the Linux kernel). But Feedly competes with its own free product and cannot see the forest for the trees.