why have car grounding strips disappeared?

Primary reason would be that vehicle electrical systems ground to the body, not to earth. They're effectively useless.

Back in the day we would often explain away customers complaints about static shocks as the fault of fiber glass belted tires. They were the cheaper alternative to steel belted tires. Maybe they were the cause or it was an excuse to upsell to steel-belts.

My Espaces (several over the years) all with fibreglass bodies, often gave me a shock presumably from built up static. Food for thought - never on wet days. Never tried a grounding strip, but feel that with one, static would automatically go to earth through one rather than through me.