Air travel is safe because it has hard and fast standardized checklists, so airline personnel don't have to make shit up as they go along. They always follow the standard procedure.
Suppose a tablet gets jammed into a passenger seat. The procedure is that a flight attendant retrieves the device from the seat and inspects it. If it appears OK they can give it back to the passenger, but if it's damaged, say the chassis is bent, they'll put it in a special fireproof bag, and the flight continues.
What if they can't get the tablet out of the seat, so they can't inspect it? How are they supposed to decide whether it's safe? If it's an iPad, given Apple's build quality and engineering it's probably fine to leave it there, but suppose it's an ATOZEE or BYYBUO brand tablet -- one of those weird brands on Temu or Amazon Marketplace that slap their name on garbage from a random Chinese factories and then disappear if there's trouble and the get sued. No way you should trust one of those.
Clearly they can't be expected to know which devices are well-engineered, and which aren't. They can't know which devices may have recalls due to battery problems. They can't even trust the passenger's description of his tablet as an "iPad". Maybe that's what he calls all tablets.
The flight attendants need a decision tree, every leaf of that tree has to be safe, it can't require them to have personal knowledge of the quality and safety of every brand and model of device on the market, and it can't require them to take anything the passenger says for granted. That means you treat every tablet you can't retrieve and expect as a cheap piece of Chinese white label shit. From time to time that'll inconvenience hundreds of people for something that's 99.9% likely to be fine, but that's how airline safety works. A 0.1% chance of an unquenchable fire in the cabin is treated like a big deal.