Although there are fully completed profiles and CVS of professors out there on university websites, although we have systems like lab rotations at universities which actively encourage scholars to try out labs and groups and supervisors before actually signing up for a PhD , although there are orientation programs and so many other services provided for helping scholars find a best fit supervisor, why does still a mismatch between a supervisor and a scholar take place which had even lead to high attrition rates of PhD ???? Where are we lagging????

you know people for real only after you spend significant amount of time with them. Short-term visits can give an indication but it is never a 100% predictor of the reality.

Not to mention most people (whether supervisor or supervisee) are good at putting on masks revealing only what is appealing. The masks hardly stand the test of time though.

c'est la vie

I also think that very few prospective PhD students can foresee what doing a PhD is really like. Doing well on a taught course doesn't mean that you'll necessarily thrive on or enjoy doing a PhD. Supervisors can't change the realities of it, and it does mean some who are unsuited to independent research will fail upgrades. If that happens, it's easier psychologically to blame everyone but yourself. Similarly, students' situations change - ill-health, interests, career ideas - there are many things that prevent completion however good the supervisory relationship is. In other words attrition rates are also if not more about student performance and circumstances, as you can change supervisors but it's not so easy to fix other things.