Back in the day there seemed to be an surplus in the supply of 6mm copper G/Y cable.
Less facetious, the proportion of conducting incoming gas/water mains supplies was much higher and the regs were written to reflect the norm, it became easier just to assume they were extraneous and bond everything and without RCDs , supplementary bond everything else.
No need to stop and think, bond it all and let God decide.
Anything built in the last 30-40 years has switched to plastic mains incomers along with a significant proportion of upgrades and RCDs removing the liklihood of extraneous paths and the necessity for bondage.
So now the norm is not to bond unless required which forces the spark to understand the reasoning and theory behind bonding as they now have to justify its omission.
A lot of old sparks will still bond and even supplementary bond as they never had to understand the requirements, they just needed to know it needed doing and how, not the why.
The problem arises when one of these older sparks is supervising a new spark who hasn't bonded and knows it was not required.
This is where their pride tests your diplomacy and technical knowledge, good luck there!