Native phone apps are more invasive and can therefore be used for more extensive tracking and spying, which is good for ad revenue. Remember how all the largest spying products like Instagram, Facebook, LinkedIn, Reddit, Twitter, etc aggressively push you to install their phone apps even though they are (or were) perfectly usable through their mobile websites.
Also there is no app store on the web, no 30% fee. So no incentive for mobile platform owners to make it first class citizen.
For example on desktop the top 10% or so of the screen is taken up by the browsers UI and tabs which is normally fine. On a tablet in keyboard mode your left with ~40% of the screen being useable. Native applications sidestep this by not needing the browsers UI.