1) Smartphones regularly have an empty battery, which would mean you then couldn’t open your lock.
2) Wi-Fi and Bluetooth signals are not at all secure and can be hacked from great distances.
3) With a smartphone, you have no proof your bicycle was locked for insurance purposes.
4) In rural areas, there are still many places with no or poor reception, leaving you high and dry.
5) You would not be able to lend anyone your bike without giving them your phone too, which is of course not very practical.
6) With a smartphone, you still need to undertake an action to instruct the lock to open, meaning you still need your hands to open the lock.