Why are old cars undependable?
Old cars are not undependable. Dependability starts with the owner. If he does not make the repairs caused by age and time the machine cannot be expected to offer dependability. There are no undependable cars just undependable people. Classic car owners must invest in their car to keep running, safe, and fun to drive.
After 30 years servicing selling and owning classic and antique cars I have determined that even a car in perfect mechanical condition, may seem undependable because the drivers are unaware of the protocol starting and driving old cars. With an old car, you may have to wait for the fuel pump to build pressure. The choke must be manually engaged and you may have to pump the accelerator a few times. In new cars, you get in turn the key and go.
My father loves driving these old classic cars. One time when he was driving a 1973 Jaguar XKE with no issues he gets in and goes to see my siblings from Tampa to Orlando.
My brother then takes the car for a test drive. He stops at the local convenience store and then when he tries to start the car it won't restart. After a bit, he calls my father and advises the car won't start and maybe a low battery but, the real problem is he is not giving it a chance to start. He is letting go of the key too, soon because he thinks the starter is making a funny noise. So, my father tells him there is nothing wrong just give it a little gas and crank it over and sure enough it started right up.
The point here is when asked if the car was cranking he said no but, it was cranking it was not starting. Having a fundamental understanding of old cars is a must in the classic car world.