I've changed a couple of dozen bike tires and never had trouble with this before, but the last three tires have been a nightmare.
Yeah, I know a big compressor always works, kinda hard to carry one without a sidecar or trailer. Cycle Pump fails to do the job, but that's what I carry.
I broke the ratchet on two ratchet straps, used WD40/soapywater/LemonPledge to try to seal the gap, took the valve stem out, let the tire sit in the sun on an 82 degree day, bounced it, sat on it, kicked it, cursed, waved a chicken along with the incantation, cursed again -- no go.
So what's the secret?