What was a major drawback of the Bohr model that caused scientists to replace it?
Two major drawbacks of the Bohr's model are as follows -
1) According the the uncertainty principle, the exact position and momentum of an electron is indeterminate and hence the concept of definite paths (as given by Bohr's model) is out if question.
2) It couldn't be extended to multi-electron systems.
Also, the Bohr's theory couldn't explain the fine structure of hydrogen spectrum and splitting of spectral lines due to an external electric field (Stark effect) or magnetic field (Zeeman effect).
It couldn't explain why some lines on the spectra where brighter than the others, i.e., why are some transitions in the atom more favourable than the others.