Some conventions do. The issue is speed, quantity of printers, and whether or not the shipping costs literally outweigh the incremental yearly cost of buying your own. Card printers are especially fragile compared to zebra label printers.
Typically a once to twice-a-year event for many conventions. These are extremely volunteer-led conventions, so a lot of financials just aren't there to support hundreds of dollars for a short term rental for an event weekend. We're out here for the love of the con(vention) pouring our own funds into things for the most part.
Some conventions can be only a couple hundred people (or less!) as fledgling conferences, so getting the costs per-attendee as cheap as possible out of the gates is important. I could see myself donating Zebra label printers into a convention to support the cause if they executed something like this.
One thing to add though: Have a "DR" (Didn't Realize) plan when you run out of your pre-printed card stock. You may find out your convention gets too popular and you run out of cards - you may need to consider having a backup available (such as printing and laminating color 'badges' to hand to your daypasses, for instance).
Some conventions can be only a couple hundred people (or less!) as fledgling conferences, so getting the costs per-attendee as cheap as possible out of the gates is important. I could see myself donating Zebra label printers into a convention to support the cause if they executed something like this.
One thing to add though: Have a "DR" (Didn't Realize) plan when you run out of your pre-printed card stock. You may find out your convention gets too popular and you run out of cards - you may need to consider having a backup available (such as printing and laminating color 'badges' to hand to your daypasses, for instance).