IBMPEERS is absent in ArcaOS. Samba client is installed instead.
IBMPEERS is not missing, you simply did not select the option, when it was presented, or you chose the easy install, which doesn't always make the best choices, but usually works properly.
WHY IBMPEERS is disabled by default?
I don't speak for Arca Noare, but it is simply that SAMBA is far better. Try to copy a 2.5 GB file, or attach to a win 10 network, with IBMPEERS. It isn't going to work. You can still attach to an IBMPEERS network, using the SAMBA client, but you may need to tweak the security stuff (basically turn it off) to be able to do it. It is documented.
Who made the decision?
Those who understand what modern networking is all about.
The original poster asked how to network with eCS 2.2 running IBMPEERS. SAMBA cannot do this. If you try, you'll see a few files, but if the number of files you examine exceeds a couple of hundred, you'll find that SAMBA has failed. Bitwise says SAMBA does not support IBM File and Print Sharing.
OS/2 is not about modern networking. It's about keeping support for a legacy system. If it can also do modern networking, that's a bonus.
I don't think ArcaOS is any different than eCS in supporting the original OS/2 File and Print Client, or IBM Peer Networking.
I welcome SAMBA and will enjoy having the server upgraded to version 4 if that gets done. I think the version 4 client must be good for someone, but most who use multiple Operating Systems on a LAN are going to choose to sit on some other desktop, so the SAMBA Server component is the one that wants upgrading.
As it is, with Samba Server version 3 and Samba Client version 4, there is a little awkwardness in setting up security for a LAN with all ArcaOS computers. IBMPEERS is easier to use and better documented than SAMBA for this case. That said, I use SAMBA for my mixed ArcaOS and eCS LAN.