If we had an infinite supply of sustainable fuels that might make sense, but we don't. So we will have to use them wherever they are most efficient or where we do not have good alternatives.

Electric cars today are already a viable alternative to those with ICEs. So there is no need to use our limited supply there. In the same way it wouldn't make sense to use them for something like heating, as the production of those fuels wastes energy and we have viable solutions like heat pumps that do not require them.

There are on the other hand areas that have different requirements. For example in the airline industry energy densitiy is way more important, so until we have batteries that can match fossil/sustainable fuels those are much better used there. Another example are industries that actually use them as resources beyond just as a source of energy, like steel or fertilizer production.