Suborbital is like building a little 2-seater Cessna. Orbital is like bulding a Boeing 777. Actually, no, it's much harder than that.

Just look at the size of the vehicles to get a sense.

If you are interested, read-up on what it takes to escape into space and then to orbits as high as 22,000 miles.

Beyond that, landing a first stage from orbital escape delivery of the second stage is harder than landing from zero velocity suborbital.

And then, add to that landing from orbital delivery to an orbit that leaves you no choice but to land on a postage stamp sized barge and, yeah, there really is no comparison.

Also, for a basic understanding of the physics at work, he could also try Kerbal Space Program. Its been one of the best tools to teach me of escape velocities, suborbit vs orbit, etc. Its not exact but very good at explaining the principal behind all the rules of physics.

A good read from the inimitable What If: https://what-if.xkcd.com/58/

Suborbital is so much easier and cheaper than orbital, it isn't funny. I think that is the reason, in a nutshell.

They appear to be trying to gain experience, while creating a new market that doesn't have a lot of competition. Bezos has mentioned that this rocket is quite similar to what they'll use for an upper stage of an orbital rocket.