Last time I checked, buses run in pre-determined routes.
Don't work nights myself but I'd imagine:
If you're drunk and need to get home quick (with takeaway food/partner), you're more likely to get a taxi to your front door rather than walk 10-15mins from the bus stop.
Also, can't see too many women walking home in the dark from the bus stop.
Taxi's aren't too expensive if there's 3 or 4 people sharing. I think a normal bus fare is €3 or more now!