Costco is making a big deal about my 88H load index tires.

Costco is just too busy to deal with non standard installations. I ordered tires from Costco 6 months ago and had to cancel because delivery of the tires to the store was delayed. The delay wasn't the issue for me. I could wait. The issue was I could not reschedule my installation appointment. The website only allowed one to schedule 4 weeks ahead but the two nearby Costco's were booked solid. (Probably due to the winter tire rush.) I checked every once in awhile for cancellations but the pop up times didn't work for me. I guess I could've called in but this is the present. We do things online. Could do walk-in but that may be a 3 hour wait. I can only eat so much Costco samples.

There is no incentive for Costco to do anything but OEM specified work so they can streamline everything which is a net benefit to their customers, I suppose.

I went to America's Tires instead.

 

Is there something about a Prius that makes it less important than on another car?

 

Small car nope,
1 ton pickup loaded to 10,000lbs yes

 

That would be true if the small car were fitted with the same tires as the 1 ton pickup.

However, for some odd reason, the engineers of the small car put small tires on it. calculated to within a small safety margin of what's needed, the same way the engineers of the 1 ton pickup do.

For the first-generation Prius, Toyota went so far as to specify a tire size that could not possibly meet the TRA 88% normal-load safety criterion for the car. It could barely meet the 94% FMVSS test, which was enough to sell it in the US.

Later generations of Prii have used larger tires and are probably not cutting things quite so close (though I haven't repeated those calculations for the later gens). But they are certainly not so vastly overspecified that it makes any sense to say the specs don't matter.

 

I’ve never had a blowout on a small car, Trucks and Suburbans, yep all the time

Tire life on my small cars sometimes is beyond 80,000 miles,
trucks, suburbans?
Lucky to get 20,000 miles

I’m not alone in this experience.