Yes, I know why and have explained as much as I can given the restrictions in the CoC against discussing hacking. But I will try again.
1. The code is very old and dates back to the very beginning of browsers and is difficult to maintain in concerns to security issues. (Official reason given by browser companies)
2. Html code can be use to download files.
ftp://domain name/file name is obsolete.
3. A well known exploit can be used against a server by using the ftp protocol within a browser to run a script previously uploaded by the hacker to his user directory.
4. This exploit can easily be disabled by an admin that knows what they are doing with regard to locking down a server but today more and more servers on the Internet are virtual servers like Amazon Web Servers (AWS). These servers are not always run by people who know what they are doing. This means more targets for the exploit.
5. The US government in a act of incredible stupidity has decided to use services like AWS and other virtual server merchants to host government websites. AWS is a cesspool of bad guys that use virtual servers to attack other resources on the Internet.
Now I spent 18 years as an admin for an Internet Service Provider and Internet security was my life 24/7 but you are free to believe that I don't know what I am talking about if you wish.
As to why now. I was told recently by my old boss who by the way is scary smart and continuously monitors Internet security forums. That a new exploit was discovered recently by Internet security experts that makes use of the ftp function of browsers in a new way that basically can not be stopped. I don't know the details of how it works yet but ftp runs on just about every device connected to the Internet: switches, routers, firewalls. He said that all of them can be compromised or even more scary may have been compromised already. So removing the ftp code from browsers may be a case of locking the barn doors after the horses got out or it might be a stop gap measure to buy time to patch millions of devices, I don't know. We may all just wake up one day and the Internet won't work anymore.
William