Even if you're a social media company, where network effect is everything and getting into everyone's pocket matters, you can still go iOS first. Snap ran with that strategy at first, and it hardly killed the company.
Notably, that's a situation that actually matters for cross-compatibility. There's no web client for SnapChat. Hertz & Costco could point Android users to the web with few repurcussions, IMO
This is still about the actual market share. iOS being 55%+ of the market makes that strategy viable in the US. You'd start with android instead if you were to launch in Korea for instance.
Notably, that's a situation that actually matters for cross-compatibility. There's no web client for SnapChat. Hertz & Costco could point Android users to the web with few repurcussions, IMO