Mostly when I have diverted, I already had taken extra fuel. It did not change the outcome. last time I diverted, I held for over 2 hours at ARN waiting for fog to clear- it didn't and we wasted nearly 5 tonnes. We still returned to departure point having used up all our round trip fuel to get nowhere in 4 hours.
My estimation is that extra fuel, although nice to have, does not achieve half as much as people think. Personal opinions, but I get fed up with people wanting hundreds 'for Mum' to a non-delay destination on a good weather day. I used to do many long range flights from the Far East to UK with restricted minimum fuel. I never had a crisis. Ran low sometimes, but carrying extra on flights like that costs big time. I didn't feel additional was worth the cost.
Itmight be interesting to consider if you have diverted, had you already taken extra? Would carrying even more have saved the diversion? It's not as clear cut as 'carry extra=no diversion'.
This for unexpected problems of course