Literally none of my other smart home devices have 5 GHz radios - and most of them are used indoors.
I have more than a few. Leviton smart plugs are one.
Grill controllers are not inexpensive lightbulbs or plugs where the extra $1-2 represents a substantial cost increase (as a percentage of total product cost). So, why not include a dual band chipset to improve connectivity for everyone? There's almost zero downside for the consumer, it's just a couple bucks more and only increases capability.
In the end, they did, and I'm glad for it.