Number Bitcoin Full Node does not increase

I have noticed that the number of bitcoin full nodes are always in the range of 10 - 10.5k range and rarely go to a level that is significantly higher than that.

While I do understand that there is no incentives for people to run a full node, except that if you do some business that transacts with bitcoin. In that case, you would want to query the full node for your transaction confirmation, rather than relying on other nodes to provide you with the data.

The only reason i can think of is there is no incentives to run a full node, as compared to miners. However, as bitcoin populariaty grows, i would imagine the number of bitcoin full node should also grow … at least marginally ?

What are some of your thoughts ?