I asked a Dutch girlfriend if she likes it when people say "eet smakelijk." She said "no, but you have to."
"Eet smakelijk" is the Dutch equivalent of "bon appétit." It seems as if every European culture has a variant. Spain, yes; Germany, yes. I've asked people from Italy, Poland, and Sweden they all have a form of it. Romania, yes.
The usage is quite ubiquitous, with regional variations. Whatever the differences, the phrase is quite specific, and intimately connected with strong social code. Within the rules of local custom, the phrase is compulsory. Generally, if you see somebody eating and they are within the appropriate realm of familiarity, you have to wish them a good meal.
You could say that "enjoy your meal" is a literal English-language translation of eet smakelijk. But there's no corresponding tradition, so the literal translation is inapplicable. A Spanish acquaintance suggested that the reason that we don't share the custom is that the English have no cuisine.... In any case, it is not necessary in English-speaking cultures to talk about other peoples' food not compulsory, and not normal.
But in nearly every other European language (if not every one,) it's important to wish an enjoyable meal. It's often necessary to do so, in order to be polite.
You just have to accept it. You don't have to like it. You don't have to do it; but it may be awkward if you don't.
And if you don't enjoy the salutation of others because you're eating, you'll just have to get used to that.