The way the founder replied coldly and closed the GitHub issue is pretty telling. Now they're doing damage control.
It's usually better to stay away from VC funded software. They exist for the sole purpose of turning a rich guy's million dollars into 100.
Because modern web is bloatware. Too much javascript, CSS, ads and cookie popups. A phone's hardware and internet speeds are generally not as fast as a desktop. So, it takes much longer to render on a phone.
Also, a lot websites nowadays deliberately make their mobile web experience shitty (cough ** reddit cough) to force their users to install their app.