When printing with a single extruder, the build plate and extruder do not heat up at the same time. The extruder does not start until the build=plate in finished. Everything heats up at the same time with dual extruding however. Please fix this, it wastes a lot of time when printing.
There's a lot of threads on the forum about this. It's like this by default because many of the machines don't have a strong enough power supply to handle heating everything at once. If that happens, you'll get stuck where nothing ever gets all the way to the right temperature, or worse, you'll burn out the power supply (has happened to me on multiple machines).
So that's why I think it defaults to that. Of course, you can also heat everything at once if you want. You literally just move one like in the starting script. Again, there's plenty of threads about this on the forum if you need more info