I think you are combining the higher propensity for roll-over (a trait shared with most SUV's of that era) with the firestone exploding tire fiasco, which ultimately was put at the feet of Firestone, not Ford, despite Ford indeed spec'ing an unusually low pressure for the pre-facelift first gen Explorer.
The fact that these short wheelbase SUV's (Jimmy, Blazer, Explorer, Sidekick...etc) were more inclined towards rollover in the event of an evasive maneuver or correction as the result of a tire failure was exasperated by the fact that of course Ford was indeed experiencing tire failures.
15" rims with relatively high profile tires was completely normal for the era and was the case on pretty much all trucks and SUV's at the time.