Side-along Apparition probably requires more skill than just Apparating yourself.
The instructions for Apparition include “Let your yearning to enter it flood from your mind to every particle of your body.” This is probably easier if you only want to Apparate your body, rather than the body of other people too.
I believe we've seen only two wizards perform Side-along Apparition in the books. One was Professor Dumbledore, who has immense magical skill and experience. The other was Hermione, who did it as an emergency measure and when they were fugitives and didn't have much choice.
Further, we know that Apparating can be dangerous. If someone without the experience tries side-along Apparition, there's probably an even higher chance of accidents than for just Apparating themselves, and they'd be risking to injure their passengers.
It's quite possible that Amos hadn't learned how to use side-along Apparition safely.