You don't need to be a big person to run most heavy equipment as long as it's already setup and ready to operate. You do need to be strong if you're going to swap out implements and attachments because they are heavy and the hoses are not easy to connect.

But, you do need to be aware of many things at once and you need to be able to move your hands and feet in different movements while operating. Not unlike how a drummer needs to move all their limbs independently.

Not all pieced of heavy equipment are that way but many are. Plus, most people would be overwhelmed just looking at the dash of one of those rigs with all the gauges, knobs and switches.