I will say I've met a few of those. Usually guys who were well established in another career field who also wanted to do the LEO thing. I can understand the desire to serve as an LEO without walking away from a 6 figure salary, vested pension, etc. Especially if you don't know if you'll stick with it long term. Reserves can be a way to dip your toes in without throwing away your existing professional life.
I don't know any SROs, so I'll not comment there.
I know several. When I first started in LE, no one wanted a SRO job. SROs while part of the PD, were actually more overseen by the city, than the actual PD. They had this weird limbo status. Eventually we started using actual officers to fill those positions at schools... but nobody wanted them, so young officers were put in those position. When I say young, I mean less than 2 years. I though about applying, but I didn't know #$@% about being a cop, I hadn't really seen anything nor was I comfortable doing my job. So I didn't apply. Looking back, and thinking of all the stuff I've seen on the road, had I have taken that SRO job, I would've been wholly unprepared if something serious ever went down at a school.
You know who when you're a young kid and about to get into a fight, and you get the "trembles?" Well, as a young cop, you get that too... and then one day, when you're confident in your abilities, it simply stops. At that point, you've probably been in enough arguments, fight, pulled your gun on people that the task at hand takes priority over fear. Maybe that's not universal, but that how it was for me. Anyways, some SROs have never had the opportunity to get over this. Now, SROs (in the past few years) are positions that are coveted by older officers in the twilights of the careers, or mid-expereinecd officers wanting workable hours for family time. In places where young officers are SROs, or officers who have never worked the street, the fear of encountering an active shooter may overwhelm them.