Blogger has thousands of computers that they control and support - their servers. They have millions of computers that they don't control, but still try to support - our computers. They can support, to some extent, Blogger running on our computers. Their ability to support us is greatly enhanced when we can accept the responsibility for the problems that are our own.
Then there are the remote servers, to where we publish blogs by FTP. They don't own, or support those computers. Very few of them do we own or support either. When we try to FTP a blog update, and something goes wrong, what do we do? Can we check a log anywhere on the remote server? Not easily. Neither can Blogger Support.
The remote servers, that host blogs published by FTP, are computers owned and supported by third parties. Blogger Support can't get even the feedback from the third parties, that they would from us if the problem was our locally published blogs running on our computers.
Any problem with FTP publishing could be a problem either at the Blogger end, or the third party end, but Blogger Support has no access to diagnostics at the other end, so no way to tell easily. Nor can they try to repeat the problem in a laboratory test, because they don't have any idea what server you may be using.
The problem with FTP is not Blogger so much, it's Blogger having to deal with hundreds of different servers, when they publish various blogs by FTP. Each different Blogger could be publishing, by FTP, to a different server. Each different server has different issues that make the Blogger FTP publishing process less reliable, in spite of the numerous settings that Blogger requires, which you must provide when defining your blog. One of those issues is file naming conventions - and how mixed case file names are used. Another issue is path description conventions. Both of these issues may be related to server configuration policy and / or server operating system.
Maybe you never have any problem publishing to your external server by FTP, but other bloggers will have problems publishing to their servers, from time to time. By applying the principle of etiology, to this observation, we should suspect that many problems with publishing by FTP, to external servers, aren't entirely the fault of Blogger. The people who support the external servers have to get involved too, and accept some responsibility.
My earlier suspicion was that once Blogger gets Custom Domains working properly, they will drop FTP support. Or at least discourage use of publishing by FTP. Having seen their latest improvement to FTP publishing, I'm not totally convinced of that, though from a business standpoint I maintain that it's inevitable.
In the meantime, if you are trying to publish your blog by FTP, and you're having problems, it's time to dust off the old Blogger Contact form again, and be patient. Alternatively, spend some time reading Blogger Help: What should I try if I get FTP publishing errors?.