Why is there no open-collector OR-gate in the 7400 series?
I don't genuinely know the answer to your question, but I can speculate that it's because there are (quad) open-collector NAND and NOR gates, which are universal gates, and you can relatively easily synthesize an open collector OR gate from these. For example:







simulate this circuit &ndash; Schematic created using CircuitLab

Because, of course, A NOR 0 = ~A and ~(A NOR B) = A OR B