In my experience restaurants in Portugal never have tinned sardines on the menu (as a starter, in salads, in mains). They also have fresh ones in the season (around June). I have seen fancy shops in tourist areas selling only (!) tinned fish though. So I always assumed it is mostly a tourist thing.
This reminds of some years ago, when a small restaurant in Cascais (!) opened that only served microwave oven meals. Homemade, but still, not my idea of eating out. But at least they were very honest about it ;)
Another surprise for me were Patagonia's tinned fish, which were phenomenal: https://www.patagoniaprovisions.com/collections/tinned-fish.