1. Government requires 50 mile range (about 20kwh battery) in all new cars. PHEV quickly becomes the default for all models (cars, SUV, trucks). Battery supply is less of an issue (A single 80kwh Tesla battery can be used in 4 PHEV cars).
2. DC fast charging (250kw) infrastructure is built in all cities. A small PHEV battery (20kwh) + DC fast charging means battery can be completely charged in minutes, as fast as filling up a gas tank. Maybe DC fast charging could even be built right next to the gas pumps (fill up gas and battery at the same time) This makes PHEV work for those without charging at home.
3. PHEV works fine in all weather. Battery range drops during winter? Just use some more gas, there's no range anxiety.
4. People get used to the feeling of driving in EV mode. And they notice how nice and quiet it is compared to when the ICE warms up. Also the environmental benefits.
5. Car manufacturers and battery companies get solid state batteries ready for mass production. Now is the time for 300 miles+ full EV cars. With solid state, no cold weather problems, much faster charge rate, no fire risk, no liquid cooling system, much higher durability. This is the battery tech that can fully replace ICE.