It's a delicate balance because Apple has to support a lot of people and at this point there are literally decades of experience showing that many people, including administrators and developers, will make mistakes or bad decisions due to social engineering or simply greed (how many people installed malware because they thought it was cheaper than paying $20 for a software license?).

SIP is a good compromise: it prevents malware from gaining completely control of the system but someone with physical access and administrator privileges can disable it for the few situations where that's desirable. That's not a high bar when you need it but it probably has a 100000:1 ratio of time preventing someone's day from getting worse to actually preventing legitimate work.