I don't think girls ever completely stopped to program, but for sure there are less girls in those kinds of subjects at higher education levels. But from my view, it all comes down to interest and I have no real explaination to why girls are less interested in computer science.
However, I can tell my story on how I got intersted and why I do not think girls at that age would have any issues having the same story.
I can only answer for my experience, but here it goes:
When I were younger (I'm still in my 20s) I started with computers and mainly to play computer games which I quickly realized was a lot of fun.
Later on, and surely labeled as a "nerd" by my fellow classmates (girls and boys) I started to take interest in cheating in games and wondered how the hell to do it. That made me walk out on the internet learning about how programs work in the first place and I discovered modding.
I understood that I can change the game data which was saved on my local hard drive in order to gain powers in the game. Cheating quickly became boring so I wanted to know how to mod a game so bosses would spawn more powerful to meet my newly crafted gear that could beat anything. So I started to mod the client with programs that were available on the net.
At this point, I barely understood all the english grammar that was used but the interest in learning on how the stuff works eventually led me to learning to program and awoken an interest I didn't even know existed. Previously to this, I had no idea how computers really worked like I had no idea how a car engine worked. I didn't examine this until I really wanted something done.
I am sure my story is like many stories in the early 00's of people who eventually learned to program. I don't think any girl that did the same during this period would have any specific attention except good ones. Maybe the girls in my school did not learn to program because they were less interested in games, maybe something else. But what I am totally conviced of, is that there were no sexism hindering these girls to learn if they wanted to. Actually, I would think that most boys would not care as much if a girl was as interested as me.
I were labeled a nerd (and had really no problems with it) but I do not think that a girl would be labeled the same. Of course there were girls labeled as nerds but not because they were interested in computers, but because they did "too much homework" or "took school too seriously". The funny thing is that I were not labeled as a nerd because of my interest in computers, I am pretty convinced that it was only because that I had a nerdy look and sat a lot in front of computers. In fact, most of them when I showed some tricks were actually impressed and had no issues with that. Children can't hate on something they do not understand and in my experience a kid always goes on the visual things or very basic information that they do understand (i.e. do too much homework / sit a lot in front of computers).
I am sure there are some sexism out there still, but in my experience the sexism has been reversed. I have always felt "second picked" or less important because of my gender. I don't understand why girls need "extra attention" regarding computer interest anymore and I actually think it's damaging for several reasons.
My question remains the same, why can't we just try to treat everyone equally?