Windows has a much harsher approach to file locking than Linux and backup software like BackBlaze absolutely should be making use of it (lest they back up files that are being modified while they back them up), but that also means that the software effectively has to ask the OS each time to lock the file, then release the lock when the software is done with it. With a large amount of files, that does stack up.

Linux file locking is to put it mildly, deficient. Most software doesn't even bother acquiring locks in the first place. Piling further onto that, basically nobody actually uses POSIX locks because the API has some very heavy footguns (most notably, every lock on a file is released whenever any close() for that file is called, even if another component of the same process is also having a second lock open). Most Linux file locks instead work on the honor system; you create a file called filename.lock in the same directory as the file you're working on, and then any software that detects the filename.lock file exists should stop reading the file.

Nobody using file locks is probably the bigger reason why Linux chokes less on fast iteration than Windows, given that Windows is slow with loads of files even when you aren't running a virus scanner.