Resistive heating is indeed almost 100% efficient, but combustion is only about 90% efficient and that's using modern technology to scrape almost everything we can, which has a cost in terms of the product upfront cost and maintenance. The reason it's not much higher is that we must vent the exhaust gases. If you were OK with the burned gas vapours in your home you could get close to 100%, but they're poisonous and so they must be vented to the atmosphere where they only cause global warming. Venting those gases means losing heat, so that's inefficient.

For the EVs in particular, because motion <=> electrical energy is almost the same either direction (a dynamo and an electric motor are almost identical) we get regenerative braking in most applications. This isn't anywhere close to 100% effective, and of course we net losses from resistance which gets much worse as speed increases - but it's not nothing.

The big win is that global warming problem. Electrifying consumption means fungibility. In my lifetime the UK went from mostly coal electricity, to no coal at all. But few cared because to the end users it's the same electricity regardless of how it was made, and most people probably didn't even notice. So if you move consumption to electricity then the generation problem is de-coupled and can be addressed separately.