I can't see why it would be a brake line issue. If there was an inconsistency in the crimping , enough to let air in, then surely it would be enough to let brake fluid, under pressure, out.
IMO, there are only two places that could potentially allow air Ingres. Master cylinder or calliper seals.
Over heating of fluid may cause it to boil and loose consistency, but would not introduce air into the system. Once it stops boiling, gases would be reabsorbed into the fluid.
My 2003 Suzuki SV1000 clutch fluid used to discolour on a regular basis. It turned out that chain lube/grime was being sucked past the seal, each time the slave cylinder was being actuated. There were work arounds available, but they involved machining a recess and an additional wiper o-ring. But the issue was due to a design flaw.
If Triumph were to admit that the master cylinders were a problem, a recall would cost them dearly. Parts and labour, loss of sales of new bikes and damage to the Brand. All of these factors come into play in their decision on how to deal with the issue.
It's an issue that they are obliged to deal with under warranty, but in their economic eyes, bleeding the system rectifies the issue and satisfies their duty of care.
I worked for a company that bought a particular sensor from China, replacing a know quality sensor, because of economics.
The new sensors cost the company $6 instead of $12, for the quality one.
When you buy a container full, it's a huge saving.
We, the technicians, proceeded to install these new sensors in the field, replacing old faulty units and new installs, nation wide.
The cheap units soon failed and proved to be a poor investment, but the company honoured warranty and continued to deploy them into the field. Technicians scratching their heads as to why we were still using these poor quality units. Customers being upset at failures of a product that they had paid good money for.
They continued to be deployed until all stock was used up and only then did the company switch to a better quality and more expensive unit.
In economic terms, it cost them more money in warranty replacement, both labour and parts, than it would have cost to scrap the entire stock. But in the magical world of accounting, it made sense on someone's pie chart.
It seems that customer satisfaction is very low on the priority scale, these days.