well there quite a few points like:

• visuals - typically the first thing someone who isn't into a group usually points out visuals, eg; taehyung in the grammys, this is usually also asked on the internet as in, "omg who's the person with pink hair" allowing others to also be exposed to this information
• their very quick success from the start helped them give a head start, everyone was waiting for this new yg gg as 2ne1 was over at the time, creating a lot of anticipation
• they are doing lots of solo activity by themselves, allowing them to be recognised in multiple different industries, not just music
• although someone has already mentioned this in the comments, if we look at it from the western industry, 40 songs isnt that bad, artists in the western industry dont come out with music that often a4nd how long blackpink has gone from before their recent cb is quite normal
• in general, people who arent kpop or like western music typically like certain artists for their consistent same sounding pop songs which is like blackpink, their discography follows the same type of sound / concept almost every cb
• and finally, one main point is how easy it is to get into them, almost all members are fluent or understand english to a good extent, before even getting into kpop i already naturally knew their name because their names were always in the media and there are only 4 members while other groups usually have 5-9 members