I still think it was killed by the Nextel merger. Both were great before that, and the golem that emerged was… not
A little bit old owners trying to hit a target for employee retention to get their full bonus, a little bit new owners finding cooperative grist for the machine.
No one in leadership had intent to ensure a minimum number of jobs.
It all depends on the stage of the companies. When companies are still in growth mode it can create more revenue and jobs. When companies run out of ways to grow (mature industries like telecom) then mergers are almost always about economies of scale and cost savings.
Yes, Google Video was similar sized to YouTube (maybe), but Google itself was far greater.
If you're bought out, the bigger company that now owns you can put more money behind your product vision and that leads to more employment.
Mergers only happen between 'equals', and in that case the benefit is the two companies can stop fighting each other in the market and 'synergize' by firing all the sales, middle-manages, and customer support that now are unnecessarily overlapped. Do you really need two sales guys to target the same customer now that you're the same company? No.