It's pretty standard that if a company is acquired for stock, the options in the acquired company are replaced by equivalent options in the acquiring company.
The converted options add to the total number of employee options outstanding in the acquiring company and thereby reduce the number of options than can be issued subsequently while remaining within the authorized limit previously approved by shareholders of the acquiring company.
All told, however, I think acquiring companies’ bias in favor of a cash deal stems from the reason described in #msg-95205794 more than the stock-option issue.
“The efficient-market hypothesis may be the foremost piece of B.S. ever promulgated in any area of human knowledge!”