Why has lpg been forgotten about?

[OldGermanHeaps]

With all this sudden backlash over diesels and NOx, and the higher co2 output and higher fuel costs of petrol why isn't log seeing more of a resurgance? Last figures i seen was the same engine unmodified running on lpg compared to petrol emitted 11% less co2 and 26% less NOx and optimising timing and compression for lpg and new lpli technologies could improve that further so why has it been forgotten as a road fuel to bridge the gap until EVs mature a bit more?
I'm giving serious consideration to doing an e500 or e55 amg estate on lpg, never had a bit of bother on the e32 735 and e38 740 on lpg before. Well, other than the usual big bmw borkage