From an economic and support viewpoint, it makes more sense for Blogger to concentrate its attention on Custom Domain publishing, where they control everything but the domain directory process, and can eliminate the uncertainty of supporting communications with hundreds of third party servers, complicated by geographical and network distance issues.
Blogger, in FTP vs. Custom Domains, last year, provided their view of why custom domain publishing has more future.
As I've dug in over the last few weeks on issues relating to FTP, as often as not the problems were not Blogger-related but were a byproduct of a webhost implementing stricter security on FTP logins (only whitelisting certain IP addresses, for instance, or throttling access for certain users). These are notoriously hard to isolate, particularly when they involve coordinating support with a third party. No one - including us! - enjoys the terrible back and forth of "it's the webhost's issue" "no, it's Blogger's issue" "no, we're pretty sure it's the webhost's issue" when all you want is to be able to post to your blog.
I've written numerous articles about various problems with FTP Publishing - some problems directly attributed to changes by remote server support staff, others suspected to be related to changes - but not proven. Many problems have been fixed by Blogger Support. So I sort of had an idea that problems existed, but what I was seeing - and suspecting - was merely the tip of the iceberg.
In Deprecating FTP, we see statistics
FTP remains a significant drain on our ability to improve Blogger: only .5% of active blogs are published via FTP — yet the percentage of our engineering resources devoted to supporting FTP vastly exceeds that.
In The Technical Side of FTP, we see even stronger details.
Google runs many datacenters, and Blogger runs in several of them. Each datacenter has a different Internet address (a.k.a. "IP address") when it connects to your FTP server, so if your hosting service requires an IP whitelist, you would have to list all of the IP addresses associated with each of our active datacenters. ... This leads to a significant amount of user frustration, and regularly results in blogs failing to publish successfully. Diagnosing these issues has taken up a large part of our engineering and support team's time.and
In a great deal of cases, FTP publishing works but is extremely slow due to shared hosting plans having slow or limited network or disk per user. We have seen cases of full FTP republishes taking over a month, entirely due to the FTP server being slow.and even a concluding
We spent a significant amount of engineering time improving FTP support in the last two years, not including support and troubleshooting user issues. Even after this effort, approximately 10% of all FTP publishes fail.
So you see, folks, when you saw the well known error
Publishing your blog is taking longer than expected ...you weren't alone. Blogger engineers were seeing it, too - from a different, and equally, frustrating viewpoint.