I must take issue with several comments here.
The F-122 is not all that hard to find in the low-$100 price point, but it does take some work, including a $20 Soarer's Teensy and probably cutting a new foam mat. The first time, these things are quite challenging, but then they become mundane, if still tedious. And even an F-122 weighs only 8.25 lb / 3.75 kg.
I now have an F-107 that is both smaller and lighter than an F-122 (the metal case is actually rather lightweight) although it does require an xwhatsit and lacks the upper row(s) of function keys.
If you can sort out the function keys on the left, the F-77 would be a near-ideal choice.
Sorry, it's hard to meticulously fact check everything to your standards posting from a phone.
Interesting on the 107 weight, I got about 10lbs weighing Bertha(which is what I was thinking of with '12lb boat', which is also meant to be somewhat hyperbole since I haven't found an exact figure for the weight anywhere online in the past), but I don't have a highly accurate scale that will go high enough or take something that size so it's admittedly a rough figure. Regardless of the exact weight, the point stands - Most people do not want giant boat keyboards that weigh a ton. Hell, if the F-107 or F-122 weighed half a pound most people wouldn't want it just on size alone. People even take exception to the size of the Kishsaver.
Or the time cost of restoring the F-122s you see crop up on ebay from time to time(Last time I went looking before today a few weeks back there weren't any; just M 122s). There's a decent one up right now along with three gross-as-hell ones, but at any given moment your choices are likely to be expensive to begin with, not in working order, and filthy beyond belief - Not a project most look forward to or necessarily have the time for. And even then given the lack of love for fullsize in the hobby people are probably still going to go for a cheap XT to noodle about with just because it's smaller.
The F-77 is a good approximation of a TKL, yes, without the function row, which can be solved by mapping a Fn layer with them. Admittedly awkward if you need dedicated Fn keys. The problem is that it's, as I noted, unobtanium. They just don't show up, which leaves the difficult-to-come-by Kishsaver and the relatively common but huge and expensive 107. (Which solves some of the FN key problems as you can slap most of them on the left hand bank of keys, but still not all of them, and most people are going to need a bigger desk to use a 107. I actually had to extend my keyboard tray to have room for Bertha and my mouse.)
The thing still remains that the entry barrier is on the higher end, be it cost, availability, or time/skill. Want one that just works? You can get a pre-converted F-107, it's what I did since I have poor coordination for working with things and little experience soldering, but it will cost you. Want a cheap one? Enjoy the funky layout of the XT and needing to clean it and get a converter. Want a full-size? Enjoy expense or tedious restoration work. Want a 60%? Enjoy waiting for one to come up and spending lots of money. Want a TKL? ...I'm sorry. XD;
But yes, degrading foam, up to 30+ years of filth, dirty PCBs, etc. Chances are really good you can make it work eventually, but it's going to be a pain. And work does have a cost - Getting or making a convertor; or getting and soldering in an xwhatsit controller depending, if you didn't already own a soldering iron(And not everyone in the hobby does yet) getting one and learning to use it, time spent cleaning, time spent punching holes in foam, cleaning, etc. Even the time has a cost. So much easier to get an MX or Topre or Matias board that just works out of the box and doesn't have decades of grime.
