That's just lazy...or they are sadly lacking skill
There are lots of Body Shop supply houses that have something if not identical then very similar to that inner liner.
And, if you have even a hint of skill with an extractor of fein knife, no problemo -You can get the glass out rather easily without damaging them.
On the other hand...the old way of mounting W/S's that had the wire heater were mounted with a fairly pliable material called butyl. Using butyl you can leave that strip in with no worries because the butyl is the weakest link. But note - No car made today for the US would have a WS installed with butyl. And in the few vehicles that still do use it as a sealant for back-glass, vent, and quarter-glass, these pieces actually bolt on the car and the butyl serves only as a sealant.
I don't personally know of anyone that has to warranty the safety and or "water-tightness" of a WS installation that will use butyl anymore. Instead we all "glue" it in using urethane. In this case, removing that strip does make for a safer install because the exposed pinch weld is a MUCH more stable bonding surface and there's more of it. The job can be done with it in there, but that strip must be perfectly cleaned and then primed with the correct primer. All of which is a MAJOR pita. Once you do all of that, now your brand new glass is mostly bonded to a 30 year old piece of rubber and plastic. IMHO it's better to just replace it - if it must be put back to OE.
I've done both of mine, one with the strip left in. And one with the strip removed. The one with the strip removed gives almost 1/4 more bonding surface. I like that. But the other one does look much nicer from inside. So the choice is "greater safety" or "looks better"
Why urethane instead if butyl anyway? With the advent of second generation airbags, the bag first comes straight up hits the w/s and then fills up the space in front of the passenger. If the windshield bond failed, the airbag would be useless at best and possibly may even make a more dangerous, even lethal, situation at worst
If you need a w/s and want that strip, I'd make sure you discuss that with the tech and tell them you want it replaced. If they say they can't find it, check with Matt, I bet he can source some. And make sure they use the right primer for whatever material it is. That's very important - for safety's sake.
T
Having trouble now whether to get er' done or spend some money at Midwest during the gone racing sale