It's more the intrusion from these random pop-ups that often fill the whole screen on my phone whilst interrupting what I'm doing on this site, that I find really jarring.
I don't enter competitions willy-nilly, so I haven't won any prizes (in the most recent case a Dyson), so it's got to be a scam.
Plus it's really beyond me how such a big global household name like Google can really get away with such things, even if they're not actually sanctioning such practices themselves, and inadvertently risking their corporate reputation.
Alternatively, it could be some online villains 'posing' as Google, of which the 'real' Google seriously need to bring to book before something really nasty happens!
But as others have said upthread, these dubious things are best ignored and avoided like the plague, plus I only decide to go out and buy things if I really want or need them.