Get yourself checked for Periodontitis [1]. (Assuming the bruxism is self-diagnosed based on your lack of dental practice visits.)
This is a common condition whereby bacteria get between the gum and teeth. It starts with sticky "plaque" from food and saliva, which hardens into tartar, which can get below the gumline. Bacteria grows in the tartar, which in time causes inflammation. At this point the damage isn't permanent and will be fixed by a dental clean. The inflammation causes swollen gums, which may be sore when brushed, and in the longer term the bone around your teeth recedes away from the inflammation. The receding bone leaves gaps around the teeth, which exposes their roots, making them sensitive, and the gaps exacerbate the condition by providing the bacteria a difficult to clean safe harbour. At this point the damage is becoming permanent, but treatment can prevent it from becoming worse. Left untreated over a period of years, the bone recedes so much that your teeth become loose, eventually falling out. End game is false teeth or equivalent. It's possible for the swollen gums to cover up the other symptoms by the swelling gums temporarily filling the gaps left by receding bone. The disease progresses over many years, so it's easy to ignore until there are permanent effects, but early treatment (a dental clean) will make it go away.
In the years before permanent damage the only symptom can be an occasional gum soreness which goes away after a few days and doesn't seem worth worrying about.
As far as I can make out, brushing delays Periodontitis by slowing tartar buildup, but over a period of many years it's not enough and one has to eventually go to a dentist to get the tartar scraped off, so Periodontitis causing bacteria have less places to live. Basically no dental visits over a period of many years with a typical diet = Periodontitis with permanent effects.
[1] https://www.healthline.com/health/periodontitis