[caconym_]

It's a new commercially viable rocket engine (not a pork-barrel jobs program) of a size suitable for serious heavy-lift applications, designed and built in America.

Obviously SpaceX is doing similar things, but Merlin, Raptor, and the BE-4 are all part of a pretty exclusive club. I don't know why SpaceX chose to go with a greater number of smaller engines for their planned heavy lifter; I imagine it might be something to do with the difficulty of building bigger engines scaling non-linearly, and the fact that modern analysis and engineering ought to give us some advantages relative to the last time someone tried to make a really big rocket with a lot of little engines (Soviet N1).

[DuskStar]

That, and it's a lot easier to shut off 90% of your engines and land at 50% thrust than it is to design an engine that will run at 5% thrust.

Oh, and if your engine is small enough, you can also use the same design on your upper stages - otherwise you need to design two engines.

Also, it may be worth pointing out that the current planned thrust for the Raptor is ~1,700kN at sea level, while the BE-4 is ~2,450 kN. They aren't actually that different - it's just BFR is massive.