Basically, people stopped posting as the algorithm started taking control of your feed.
I discovered FB purity [1] recently, which does cut down on the algorithm's spam in your feed. But it turns out people have already moved on.
£2/month would have been a tempting proposition 7-8 years ago. But £4/month in 2025 makes no sense. It is only offered to make the regulators happy.
[1] https://www.fbpurity.com/