Craigslist is one of the best pages on the internet. It's functional, it loads fast, it doesn't have a stack built of buzzwords and bullshit. It works on every device everywhere. I mean, what business does a page have being megabytes and megabytes if it's gonna display a couple bytes of text? None. It doesn't matter if it's "technically free" these days, that's just bad design and engineering.
I agree with you, but I still think they could benefit from at least having an app that loads their website. Craigslist is represented in app-stores by unofficial 3rd party apps that aren't very good. Users may have bad experiences with those apps, which Craigslist may want to prevent or control.
Some people might think (incorrectly) that their lack of presence in app stores means the company isn't focused on mobile or that their platform is not intended to be used on mobile.
There are benefits to having a mobile app over just a mobile website, such as mobile notifications, consistent/better authentication, being featured on users' home screens (next to LetGo, OfferUp, etc.) instead of hidden away in a web browser app. I would think that Craigslist would find their users to be more engaged with an app.
Craiglist design actually sucks. When I first used it, the whole thing was almost revolting from design perspective. Where some people see simplicity, others see utter lack of modernity, friendliness and affordability. I still can't get some of my relative to use it (they ask me to post on their behalf!). Before you cite page counts, revenues and unique users, think about how many people are not using it despite the fact everyone has heard about it and everyone has a need to sell something on and off. Amazon UX is almost complete opposite of craiglist but is usable by much much wider audience.
I mean, we can't prove who "isn't" using it. We can prove that millions and millions of people are using it and seem to be content with it; we can provide anecdotal accounts (including by many people in this thread) that the simplicity and straightforwardness and consistency is what brings them back to the site. I can tell you that everyone I know looks at Craigslist when they're looking for apartments. But I get that you don't like it; I just think you need to acknowledge that's a preference, rather than an objective fact.
I use CL to advertise for my manufacturing business. It delivers 95% of our customers to our online store, and it does it for a monthly advertising budget of $270. We have $15-30k monthly revenue from these customers.
I like websites that don't change. I can come back to Craigslist once or twice a year, year after year, and it's exactly what I remembered. No hunting around, no discovering new gestures and behaviors. It's simple, obvious, and it for what it does, it works.
Just imagine the number of people that would immediately reject craigslist if it got a clever 'redesign.' It has worked the same way is forever and there are people who are not incredibly computer literate who rely on it. If craigslist moved as fast as facebook then in my opinion I think it would have been already been replaced.
The mobile site is really good. Hell, even the regular site has incredible usability and is very lightweight. It might not look as pretty as GumTree, but it's very usable.