As others have said above...
Would be interesting to see how much reliability has changed. I recall a lot more DNFs when I first started watching F1. If cars are struggling to maintain reliability, then I suspect they will be more likely to vary in pace during a race, hence more overtaking. Today's cars seem to be able to nail perfect lap times on every lap.
The cars seem to be much closer in pace. That hinders overtaking. You need some sort of performance differential to enable a fast car to overtake a slow car. Today's cars on similar pace rely more on driver error to allow overtaking (or banzai out-braking moves).
Remember when cars failed the 107% rule for qualifying? With that sort of diversity in performance you are bound to get more overtaking.
Having said that... If there are big performance differences then quali is going to sort the fast from the slow more effectively than today's closely paced cars?
Would be nice to see some stats on DNFs, and variation in pace from front to back of the grid.
Of course correlation is not causation
edit - typo corrected to 107%