What do expensive instruments have that cheaper ones don't? Quality control for one thing. You expect them to be problem-free and to come set up correctly from the factory or from the distributor.
Then you realize they're not set up properly at all. Then they develop problems a few months down the line. And you're left wondering if they played you for a fool.
Uh-huh. There's a watershed point for instruments, a line at which above is fine, and below you run into things like tuners not staying in tune, electronics being insufficiently shielded and bridges not intonating properly. That line used to be quite high, it is now surprisingly low. I would quite happily gig with my £109 Harley Benton.
Oh, it's still there. But I'd rather buy a set of good aftermarket tuners for my Harley Benton than spend over twice as much and realize I have to replace the tuners anyway. Or the bridge, Or the electronics.
Hell, I bought an EMG PJ GZR set for a very low budget quarter of a century old Vision bass (which actually has really high quality tuners) and it's been transformed into a completely different instrument.
As others have mentioned, I think 'POS' doesn't mean what it once did. Today, there has to be a distinction between 'low cost but solid' and 'low cost and poorly built' - the latter of which gets into POS territory. There are GREAT low-cost basses that are perfectly giggable and recordable. Then there are true POS's, which are usually the Temu/AliExpress cheapo copies of copies. I gig my SX SJB-75 and my Squier Classic Vibes right alongside my Laklands and Sadowsky without worries.
Those Aliexpress/Temu copies are horrible but that's for a different reason. They're purposefully mass-manufactured crap at the lowest possible cost with zero quality control and their cost is at most $10 a pop. They're so much crap that not even disreputable companies want their brand on them. Then they're sold on that marketplace at $100-$200 by one of the myriad sellers that appear and disappear every week. When it arrives and you immediately realize it's a lemon, the seller has long disappeared and you have zero recourse, so you just chalk it up as a loss.
When the cost rises to $100-$200, the instrument that China Co. Ltd. can churn out can be consistently high quality and that's what the budget brands use.
If a factory in China was ever paid $1,000 per instrument, they would make frighteningly excellent pieces... that nobody would buy.
And I could add, things like hardware and electronics can be replaced. If I see a cheap instrument on stage, I can assume that any of those parts have been checked and replaced if necessary
You'll never hear about it because there's an unwritten rule that professional musicians will not endorse a budget brand and budget brands cannot openly benefit from a celebrity endorsement, yet it's often an open secret.