if one looks at completion rates of any online courses (Udemy/Coursera - under 4%)
As someone with a 96+% 'failure' rate on Udemy/Coursera I honestly don't see the relevance of this statistic. Most people going to University are there primarily because they want/need the degree. That piece of paper is really valuable, perhaps even more so than the knowledge gained. The piece of 'paper' offered by Coursera/Udemy etc. has basically zero value, so the people taking those courses are doing it almost exclusively for the knowledge they offer. Once you've learned what you wanted to learn from the course there is very little incentive to go the extra mile and go for the 'completion'.
The piece of paper is valuable because it represents a sustained effort of learning over an extended period of time.
I understand how from an individual's pov what you said makes sense. Similarly I hope you understand why from the system's perspective: it's the effort that's mandated and not just the proficiency.
Employers and others (higher education orgs, etc) care a lot about sustained effort, alongside proficiency. Only proficiency-focused systems (like Udemy/Coursera/Youtube) are not respected as credentials, since they do not showcase this.
As someone with a 96+% 'failure' rate on Udemy/Coursera I honestly don't see the relevance of this statistic. Most people going to University are there primarily because they want/need the degree. That piece of paper is really valuable, perhaps even more so than the knowledge gained. The piece of 'paper' offered by Coursera/Udemy etc. has basically zero value, so the people taking those courses are doing it almost exclusively for the knowledge they offer. Once you've learned what you wanted to learn from the course there is very little incentive to go the extra mile and go for the 'completion'.