As others have noted, the Xjack was neat, but a bit fragile. I really liked my Xircom Realport[0] card - it had durable Ethernet and modem jacks, but did take up two card slots. It was great for field work.
They had double-height PCMCIA cards without the pop-out that you could directly plug into. The Apple Newton was a PCMCIA device. It wouldn't take much for manufacturers to bring it back just by including it in a new design, but that would be too convenient, right?
What I've witnessed recently is that the kids really want their buttons and switches and are sick of janky digital UI. And get a load of Apple wowing everyone with a button on the new iPhone 16! What is old is new again.
Dongle sockets were pretty fragile too. I think the most robust were the cards where there was a regular sized jack at the end of the card, but those had to stick out from the end of the laptop, and if you had two stacked slots as was once common, you wouldn't be able to use two of those.
Although my modem card didn't have this XJACK thing, it had a big chunky end that stuck out of the laptop to fit an RJ11.