On one bike, no longer in my possesion, I attached such a lock with hooks that had bolds on the other end. I used normal nuts to fix the lock to those hooks.
As it was about 30 years ago, I do not remember how and where I got hold of those hooks. I do remember that I used tape, around the frame on that point, to protect the paint and to make for a better fit.
If you feel the cable ties work for you, keep using them. You will likely not lose the lock unless all 6 fail at the same time. When the lock starts to rattle it is time to check and likely replace the ties. If you re-do all of them, you may want to tape your frame to protect it against the rub of your lock.
For longer locking, add a second lock with which you can fix your bike to a sturdy object. Your lock likely is made to add a cable and you enter it in the top of the side that is opposite of the key, not to be seen in your photo. Those come in several lengths and the longer ones seem useful. I use a separate cable lock and a friend a D lock instead.