Which we have yet to answer. We don't really need to find an answer, I can easily live without one. But for the sake of theoretical inquiry, just saying, lots of good talk above, but no actual answer to the question.
Apple judged that some iPad users would want cellular connection within their device.
Apple also judged that some folks would NOT want cellular connections, so they provided an option. And those options sold well enough that they continued to offer them without cellular.
Apple judged laptop users would not want this feature.
Makes no sense.
Well, actually it does. The form-factor of a portable computer does not make for good phone calls, unless you want a video call. Just talking to a computer does not seem intuitive, at least to me. However, Apple provided the ability to do video calling with FaceTime and avoided the extra cost of putting cellular circuits in the portable and the added cost of the user having to have a separate cell line for your portable as well as your phone. For data they gave hotspot capability. So, you CAN make a call and use cellular data for connectivity, if you want, and they didn't force it on folks who don't want the capability and who would object to the extra cost by not buying it. Plus, they avoided the complexity of their supply chain have two variants of every configuration of the MBP/MBA. The lineup is already complex without doubling it.
Unless there is some technical issue which we've yet to uncover. For instance, maybe Apple is so focused on battery time in laptops that they didn't want to make room for the cellular hardware within a laptop, preferring to use that space for the battery.
Maybe, but I suspect the cost was more of a factor than battery space.
But, somehow this wasn't an issue in the smaller iPad.
Again, makes no sense.
It does, actually, as I've described. And the smaller iPad is closer to a phone than a laptop, both in size and form-factor. If you compare an iPad mini to a iPhone XS+, the difference is size is not that great. I'm not ever going to hold a laptop up to my head to make a voice call. It's enough to laugh at someone holding up a book sized iPad to make a voice call. About the only way to use an iPad/MBP/MBA as a phone is as a hands-free, or speakerphone, which is annoying to your neighbors and has the further annoyance of picking up all kinds of background noise. I used to ask anybody who called me on a speaker phone to call me when they could use a handset. I hate the background noise on speaker phones, even now.