To a point is makes sense that they use different unit even though it is confusing since it depends on what hat you put on
Network people tend to look at data signalling. This tends to always be some form of binary so they prefer to use bits. They don't really care what type of data is actually being transmitted. It used to mostly be telephone calls when they first went from analog to digital phone and this was years before internet existed so they didn't really think of it data transfer. Although you will see network people talk about frames/packets per second when they are looking at firewall or switch throughput.
File transfers are looking at mostly data storage. Things like files sizes are all stated in bytes so it makes sense they use this term. All they really care about is how long does it take to get a file from one location to another. They tend to only care about the actual payload part of the packet and ignore a lot of the overhead inside .
This means they do not count overhead used for things like IP addresses and other header information that is wrapped around the actual data. This means even though you generally can convert 1 byte to 8 bits the data rates will be slightly lower in bytes/sec because of this extra data they are ignoring that the network people count.