Because your residency card is not considered ID. You need a cedula or passport to do some banking, open utility accounts, get points cards at the grocery store etc. If you do not have a valid cedula, when passports stop being accepted for these types of transactions, you won't have any form of acceptable ID.
We've known that the old cedulas need to be updated for quite some time now. By leaving this fundamental obligation to the end, all you've done is ensure you get caught up in the long lines. Renewal is free now but wont be forever plus the fee for letting your old one expire.
I expect you can get by without a valid cedula for the time being, but that wont always be the case. Renewing later may be more inconvenient than it is now.