^ yep exactly as EZ said.
you do three subjects at high level (which often dips into uni level, harder exams, etc.) and to get a 7/7 for psych for example (equivalent to close to a perfect score) a 65% on the exams is required (i looked at this a couple of years ago so it might have changed). Whereas other subjects for a 7 is usually ~85%
but for me to get a 99.30'ish (41/45) i would have needed (in my exams)
65%+ in HL psych, ~85% in Math, HL Bio and HL Chem(7's), 70~80% in English&Other Language(6's)
And then only a low grade on my ToK/EE (not too hard to get, which is a score of 1 on it)
Many people here would definitely be able to get 99+ more easily whilst doing IB (if you are able to score well in a science, math, english, humanities (includes psych) and second language. Although it is harder, more time-consuming, it is far more rewarding. Plus, you aren't competing against anyone else.