Misalignment of incentives
Startups, tech or otherwise, do not exist to create jobs. They exist to make money. They are *funded*, sometimes massively, to make money. If they can do so with greater automation, they will. Even for those startups that create physical things, it's more cost-effective to use pre-manufactured parts (including microcontrollers) and automated assembly than to hand-craft everything from small pieces. It's more cost-effective to sell on the internet than fight for space in a kazillion brick-and-mortar stores. Many logistics and even HR systems can be outsourced. So it's no surprise that even startups that intend to grow rapidly employ what once would have been regarded as a skeleton crew.
The thing is, if startups hire fewer people each, then maybe there should be more startups. Unfortunately, the funding models aren't geared for that. They want to fund a few unicorns not many minnows. Tax laws, accounting requirements, insurance requirements, and regulatory systems are increasingly hostile to smaller businesses, as they each tend to exact a fixed cost per company that's in the noise for a larger company but significant for a smaller one. (BTW I'm way over on the progressive end of the spectrum and support most of these things in principle, but even I recognize that their implementation has had ill effects.) If we want to undo the over-centralization (and over-financialization) of our economy and go back to a time when regular people were creating jobs for other regular people, we need to stop putting startups in the shadiest part of the garden and letting the giants stomp all over the fresh shoots.