i grew up with liberal parents in what's considered a more secular home. unlike all my peers i didn't partake in sunday school nor get a confirmation(it's like the catholic equivalent to a bar mitzvah). my grandma was very religious(and evangelical), but we didn't live close to her, so her religious ideals were rarely present in my life. but still, i only came out to my parents at 19. why? because despite all of that liberal and secular environment, i still had to witness through media all the stuff other closeted people faced when coming out. it created a little voice in the back of my head that instilled fear in me, made me worry i'd get beaten up, kicked out, sent to conversion therapy. because that's the shit that's constantly being displayed in the media. having an accepting family isn't the norm, we're considered one of the lucky ones. so it can really fuck up your perspective of things and make you fear coming out will have a negative outcome.
that is one of the big factors for coming out to the people close to you. but it also needs to be taken into account the external factors. sure, you might live in a liberal and accepting place, but that just means majority are accepting, not all. so you're still at risk of being discriminated. it might not be the level of discrimination someone might face in a more conservative environment, but it's still discrimination. and it might screw up your life a little bit. all it takes is one homophobe in the wrong place at the wrong time. europe is deemed a pretty liberal and accepting place for lgbt people, but that only applies to the big cities. go further out and you'll immediately be met with people who are openly bigoted and have no issue saying it to your face. it can make you feel less secure about where you are, feel unwelcomed, ruin job opportunities, etc.
so while growing up in a liberal/secular home, in a liberal environment might seem like recipe for a safe coming out, there's still way too many factors that create that fear and keep people in the closet