It really depends how frequently one is outside. I have had many laptops with cell chips and sim slot but never bothered to pay for a sim when I could just tether my smartphone connection, even when using the train. I usually plug the phone to the laptop if I need to charge the phone.
Do people really not use it? I use my iPad cellular all the time. Constantly.
One of these days I'm going to buy one of those old MS Surfaces with cellular and stick Linux on it. But for the installation/drivers hassles I'd have already done so.
Fun fact, I once bought a reconditionned laptop and the sim card of the previous owner was still on the slot. More interestingly I could use it to connect to the mobile network for at least 2 years without even knowing the PIN (and having reinstalled to linux).