It is easy to ask, it is nearly impossible for every partner to actually install it. Many were working in locked down environments where they would need to get some very unhelpful central IT team to approve new software and install it on workstations. Even if they could convince the central IT team to install 7zip they probably weren’t using configuration management to install it so there was a chance someone would forget to install 7zip while provisioning new workstations. Unfortunately, when you do not know who is going to consume the data you need to use the most common denominator which is still zip with deflate64.