The reason that there is thermal events with consumer units is poor inspection and testing, screws loosen over time and things degrade but rather than address the actual issues the powers that be (IET) decided to allow thermal events but contain them in a metal enclosure with all cable entries sealed. Yes it made sparkies a lot of money because when undertaking other work they just insist the main board is upgraded because it is old, outdated and a fire risk, the unscrupulous would add that now it has been pointed out and you know then your insurers would not cover.