Fortunately, in my business, incumbency is a powerful thing. It'll cost a school around a quarter million dollars to remove our hardware, install another vendor, configure their software platform, and train up their team on the new system. All to get essentially the same set of features with a slightly different UI on top.
Not many schools (or other government agencies) can make a case for that choice.
And their purchasing processes are highly structured and regulated. And audited. It turns out that being a developer and project manager in the past helps me to ensure all the i's are dotted and t's are crossed in this complex and confusing system.
Can others do it? Sure.
Is there anyone else who can do it AND who knows our products (hardware and software) inside and out? And how our security infrastructure is built? And how our third-party installers work on-site to get our equipment installed? And how to integrate our systems with around 20 or so of the other common tools in use in the market?
Yes... someone knows each of these things. But I'm the only one that knows ALL of them, and can stitch them all together into a good story that wins business.
So yeah, I can be replaced. But it takes a lot of work by a lot of people who already have full-time jobs, and many of them don't have the skills/focus to attend to the all-important details like I do.
I have no illusion that my job could end literally any day. All I need to do is make one tiny error in one part of one document and either lose a customer, commit the company to legally or fiscally disastrous terms, or promise features/functions that don't exist, and I will instantly be The Fall Guy.
I am absolutely sure that, the day I am fired, my CEO will have a negotiation with some Purchasing Manager from a State-owned Utility, or huge school district, and the conversation will include the phrase, "... I apologize for that error, and the employee responsible for making it has been fired."
Either that or I retire. That's how this job ends.