Why on earth do they endeavour to bring down security by putting biometric sensors on the phones, tablets and PCs which have been somehow protected by passwords?

Threats that can be thwarted by biometric products operated together with fallback/backup passwords can be thwarted more securely by passwords only.

Whether static, behavioural or electromagnetic, biometric products are generally operated together with a password by OR/Disjunction (as against AND/Conjunction that is common for
2-factor authentication) so that users can unlock the devices by passwords when falsely rejected by the biometric sensors. This means that the overall vulnerability of the product is the sum of the vulnerability of biometrics (x) and that of a password (y). The sum (x + y - xy) is necessarily larger than the vulnerability of a password (y), say, the devices with Touch ID and other biometric sensors are even less secure than the devices protected only by a weak password.

These biometric products might look more secure in appearance, but it is just a false sense of security. Many of the consumers, who are trapped in the false sense of security, may well be piling up more of their information assets in the cyber space while some of the criminals, who are aware that those consumers are now less secure, may well be silently waiting for the pig to be fat.

False sense of security about a threat could be even worse than the threat itself. It is a conundrum how it is possible for so many security professionals to remain indifferent to such a
nightmarish situation.