Because it is a process, I have to go on their premises and prove that they are stealing my process. You must obtain a warrant to do that (because otherwise it is trespassing), and because competitors could just willy nilly claim "you're stealing my process" in a spurious fashion to gain access to the premises (and learn about what competitors are doing), judges typically put up a very high burden of proof to issuing those warrants.
You'll effectively never be able to enforce a process patent, so you're better off never patenting it and keeping it a trade secret instead, that way you have a bit of a moat.
By contrast, for a molecule or plant patent, the existence of the product is proof of infringement, so it's easier to enforce infringement.
For a molecule patent, you do not need to disclose the method you use to make it. IANA(P)L, You might be required to disclose one way of making the molecule, but it almost certainly doesn't have to be the way that you do it "in prod".