Parts of the agreement aren’t enforceable but not everything? I’ve seen things like venue and arbitration rules established and persist in otherwise junk agree

Parts of the agreement aren’t enforceable but not everything? I’ve seen things like venue and arbitration rules established and persist in otherwise junk agreements. I see a lot of contracts from customers buying our dev services with weird language in it. The opposing counsel would have to know it not enforceable but it’s there anyway. Sometimes it’s silly stuff like “no open source software or code” yet it needs to be MEAN stack running on Ubuntu in AWS.