extreme latency for any new data fetch/processing (an http roundtrip or more for each interaction with your data)
someone else being in control of the programs you use, forcing changes and updates whenever they like, renting them as a service,
your data hostage, snooped at, sold to advertisers
a limited UI experience based on the DOM and browser APIs
crappy OS integration
(often) ads
There's a great deal of technically unnecessary complexity that many people here handwave away because "that's just how it is."
It's kind of funny how, e.g. above, the emphasis is on "UI," when that's not it at all. It's the underlying infrastructure that's often encrusted layers of unnecessary (but profitable) stupid.
Anyone who thinks UI is where the latency and complexity resides should do a 3-mo residency at a cloud provider running actual infrastructure--not VMs and the like, but the actual routers, backbone links, service provider peering, and servers. It'll change your perspective on complexity for sure.
This is a much bigger problem than people realize. Instead of working on improving user experience, we've got people explicitly working against user experience by injecting ads into it, for the simple reason that they have your attention and can then sell it. It's the attention economy, and it sucks. Fuck ads.
The trailing part that's left off is "for free". If you want all the content we receive for free today, someone has to pay for it. So either people pay with their attention or their wallet, and consumers have by and large made their choice of ad supported services over paid alternatives.
This one doesn't have much to do with online vs. offline except that you have to be online to see the "latest and greatest" ads. Stale ads can perfectly well be shown offline.
They can, but an Android app I use regularly simply won't show any ads if it cannot access the internet - I get its premium version for free just by pressing a button. Meanwhile I've seen the user-hostile version of that on an iPad years ago, where an app simply locked itself until it was able to download ads.