This is surprisingly not true of a lot of people.
I get customers coming in, combing over a specific section, not necessarily "browsing" (usually walking in, checking a section briefly, then leaving just as abruptly without a word). We politely offer help, asking if there's something they're looking for. We don't hard-sell jack (we don't have a rewards card or anything to push) but people will either say "just looking" (no you're not, we're not stupid) or ignore us altogether.
I can't speak for anyone else, but when I tell a shop assistant that I'm "just browsing/looking", I'm actually telling them to fuck off and get out my personal space. I'm just polite enough to not say that outloud to someone who is just doing their job.
As I said before, I understand why you do it, and I don't discount there are many who are greatful for attentive people trying to sell them shit.
However, if anything, it makes me want to leave your store and if I'm approached before ive even started looking around, often I will.
If I've not even made eye contact with someone and look in no way confused or lost, I feel they are divding my attention from shopping to unnecessary social interaction. Often that is unwelcome and irritating.
I think it boils down to the fact that I would never walk into a shop without a concrete idea what I want and if I am dawdling around, it means trying to " discover" something along that tbeme.
An example is yesterday, decided I wanted a pair of red and black sneakers. I don't need a shop assistant to find me red and black sneakers, I can see for myself what colours are on display. If I see a pair I like, I may then ask if they sell them in red and black, but a assistant standing at the door trying to talk to me is distracting me from scanning the store, which in a typical sneaker chain can take less than 30 seconds.
Talking to people is holding me up and isn't productive in most chains anyway. It's very rare a shop had something "in the back" that isn't displayed in store.