I find an upright makes you play in a certain way due to the ergonomics, especially the tight radius of the fingerboard and the string height and spacing.
You can emulate this on an electric bass but it's never the same. I have a Variax bass which has a very passable upright emulation but it doesn't play like an upright which I think is the main thing.
I can never copy the upright 'bounce' of a fast rockabilly style walking bassline on electric bass... And forget about copying slap.
Also apart from the playability, and this might be shallow but aren't we entertainers after all, just the physical appearance of an upright makes people smile. It adds a certain look to the band and people always comment on it or want to talk to me about it.
It's big, it's cumbersome, but totally worth it.
Maybe if I used public transport then I might look at it differently but as there's none around here I have to drive myself to every gig so it's no hardship to take the big, beautiful beast.