It's just a matter of user preference. People prefer to use Bitcoin to put their savings right now, and only OG people are using LN for selling small quantities for every day usage, like it is my case.

The reason why this happens it is very well known: Bitcoin is hard money, and nobody wants to spend it except for necessity. I see no problem on this.

The "halving" in numbers is just due to most people that before had a node now have private channels using private wallets, because they have realised that maintaining a node requires too much time that they could employ on having fun with their BTC.