I've done a lot of consulting that involved high availability and DR over the years, and companies are surprisingly much more willing to spend money on redundant infrastructure than to schedule the time to properly test it on a regular basis and make sure that money was well spent.
I can only guess those in charge figure "I signed off on paying for redundant infrastructure, if it doesn't actually work I'm off the hook and can point my finger elsewhere" so why approve testing? It worked when it was installed so it will work forever, right?
I can't count the number of "walkthroughs" and "tabletop exercises" I've seen that are claimed to count as a DR test. The only thing those are good for is making sure that housekeeping stuff like the contact and inventory list are up to date, and making sure those involved actually remember what is in the DR plan.
Clients don't like to hear it, but before go live of a DR plan I think you need to repeat the entire exercise until you can go through the plan step by step without having anyone have to do a single thing that isn't listed in the plan as their responsibility, and without anyone feeling there is any ambiguity in any step. Once you've done that, then you need to get backup/junior people (ideally with no exposure to the previous tests) to do it on their own - that's the real test that nothing has been left out or poorly documented. Depending on vacation schedules and job changes, you might be forced to rely on some of them when a disaster occurs - having them "looking over their shoulder" of their senior during a test is NOT GOOD ENOUGH.
When a disaster occurs, everyone is under a great deal of stress and steps that are left out "because they are obvious" or responsibilities that are left ambiguous are the #1 cause of problems.