The alarm systems, I kind of understand, insofar as there are
1. security certifications depending on these being present and functioning, and nobody's going to certify equipment with arbitrary third-party repairs; and
2. these devices always work only with some kind of subscription paid to a security company anyway, since the point of them is to send some signal to said company to get something to happen.
The problem is that it's basically impossible to tell when an alarm system has been working all along, vs. failed and was then repaired by a third party — including flashing it with subtly different third-party firmware found online somewhere — and now is "working" again with no visible change to behavior (but where it'll now help you commit insurance fraud.)
As such, there's no way for the insurance companies to make such a forbidding rule, and have it be enforceable. There are no "inspectors" or "auditors" that can be sent to look at your alarm system who could possibly notice that it's been "repaired" in this manner.
Pretty much the only (industry-wide) thing that can be done to curb such repair attempts, is to outlaw the tools (like reverse-engineered third-party firmware) required to do so.
(Of course, any given alarm device maker could do what Apple has done with iPhones, and just make all major components of the devices proprietary, and have all components do signing handshakes before talking to each-other, where they reject each-other unless they've both been mutually first-party signed and activated. This would put high logistical barriers in the way of repairing the device — you'd have to get your hands on first-party parts, that the OEM won't sell you. But there's no system-level incentive that either the state or the insurance companies are in position to create, that would get them to do that.)
1. security certifications depending on these being present and functioning, and nobody's going to certify equipment with arbitrary third-party repairs; and
2. these devices always work only with some kind of subscription paid to a security company anyway, since the point of them is to send some signal to said company to get something to happen.