I lucked into my first job with a startup and never had to go through the job hunt as a junior candidate (other than through a few big company mass grad hire processes which were an absolute fucking joke, and thank god I didn't actually pass any of them), but this mirrors my experience with hiring juniors.
Every time I've done it I've been inundated with candidates. You pretty much have the pick of the litter.
Personally I'd prefer to hire a lot more juniors. I think most senior front-end developers are pretty rubbish at their jobs and have spent most of an easy career on autopilot learning bad habits and bad development practices. I much prefer to work with juniors, before those "senior" (mostly enterprise and consulting) devs have got to them.
The problem is it's just not possible to train juniors the right way fast enough. I'm confident I can train almost anyone with basic programming aptitude to be a 95th percentile front-end dev, but it'll take a year or two, and my already average productivity will tank during it.
Most managers won't understand or accept that. They would, except that there's always someone else selling them the "get people productive in 2 weeks!" bullshit, which you can't compete with. Big companies (the ones with the budget to train juniors) pay a huge amount of lip service to training, but are pretty much universally bad places to actually train great devs. They're good at turning them into average consultants that get flustered with their tools and stuck all the time, because they overengineer everything and never bothered to learn from first principles. (Then they give up and pretend to work while spending 8 hours a day whinging on HN about how bad the JS ecosystem is).
And if you're doing your own thing without managers to mess it up, then you probably live and die by your productivity. Unless someone wants to throw a stack of money at you just to create great devs without accomplishing much else, then it's not gonna happen naturally.
There's other impediments too. I love working in person with juniors, but not as much as I hate commuting. And I think training juniors is one of the few things that's much harder to do remotely.
This is why there's so much demand for great devs. There's just so few of them. The industry isn't set up to train juniors, and the places that can waste the resources to do it are the ones that have environments which turn them into idiots.