Having those planes stay at envoy allows FOs to upgrade without having to change companies and domiciles. This is true even if it's short lived.

The Envoy MEC has its own negotiating landscape right now, and the bigger the seniority list, the better the possible outcome.

That being said, a DOH offer would put many of the Envoy FOs in a respectable spot on the seniority list. However, that is only focusing on what is good for the individual pilot and not necessarily the Envoy pilot group as a whole.