With a password you can have an exact binary comparison. Either you supplied the correct password or you didn't.
But with biometrics you just have an approximation because your fingerprints change slightly due to the position in which you hold them, your health, humidity, pressure and probably other stuff I'm not thinking of. So the sensor can only say that it's like 95 % or whatever sure that it got the correct fingerprint. And this uncertainty makes it much easier to exploit.
And your fingerprint is not secret. You leave it all over the place. Especially on devices you use every day. And your fingerprint can (and will) be taken without your consent. And you cannot change your fingerprint if it gets compromised.
All those spy movies showing how trivial it is to circumvent biometric security have in common that whatever method they used was realistic.