I do as I have a tester checked back to back with a calibrated garage one, I'm only doing so to see if there is even the slightest measurable degradation which based on my previous experience of multiple vehicles I dont expect.
To explain I was a teaching assistant and benevole at a Lycée pro for motor vehicle technicians, every winter for the Téléthon we would open up the workshops to recieve the publics cars for a multi-point checkover plus wash and valet.
I because of my age was tasked with driving the vehicles through the various stations manned and womanned by the students, retired people were less anxious with me driving their pride and joy than a student even though many were training to be HGV drivers.
Out of the hundreds if not thousands of the vehicles I drove through only one failed the brake fluid test done on a very expensive fixed test bench, it was a poor area with very few new and well maintained vehicles.
My vehicle went through as well so I could contribute so over a decade I kept a close eye on my brake fluid, after 12 years in my ownership (15 years old) it was moisture content wise slightly down on the day it left the factory still at the top of the scale but had become very dark so I flushed the system and replaced it, otherwise it would have gone to the scrapyard with the original fluid like most vehicles do.
The only risk these days with the well sealed master cylinders is leaving a top up tin open on the shed shelfor to owners of MK1 Ford Galaxies (RHD only) which had not been recalled where water would drain from the scuttle onto the faulty master cylinder reservour caps, enter the brake system and sink to the front calipers.
The problem were any water to be present which is only through wilfull or negligant contamination is absolutely with the fluid boiling under heavy braking having experienced it myself first hand, in the bad old days brake lines were frequently replaced after MOT failure through external rust but that also thankfully is a thing of the past. I have never ever heard of anyone replacing a brake line through internal corrosion unless it had been left open for years during a rebuild, fuel lines yes as ethanol fuels are highly hygroscopic and the tank venting and filler cap sealing not to the same degree but even that will change.
Garages and mechanics will continue to replace perfectly serviceable brake fluid because its a money earner and they can play to peoples emotions.