The following is just my own assumptions, take with a grain of salt.
Phones are often taken out to perform a quick task, then stashed back in a pocket/bag many times a day. As such, being able to unlock a phone quickly is a rather useful feature.
On the other hand, laptops are usually taken out to be used for larger tasks, and as such, do not need to be unlocked as often.
Fingerprint scanners add less value to a laptop than they do a phone.