In the olden days, most of the things in the aircraft were done by the captain. From the cockpit preparation to engine start to taxi, it was all a part of the captain’s job profile. The first office It was quite the norm. The taxi phase of the flight is quite critical and it has, it and can lead to a disaster, if you are at the wrong place at the wrong time. So, it was very natural for the airlines to make a rule which stated that it is only the captain that taxied the aircraft. The captain, most of the times being the more experienced pilot and being the legal commander of the aircraft, it was natural for him or her to handle the critical phases of flight.
The tiller on most Boeing 737s is on the left for this reason. The captain seats on the left side and as the first officer does not taxi, only one tiller is enough. Adding another tiller for the right side pilot is of no use. So, it was a cost cutting measure. If you have read the start of this paragraph, you would have noticed that I used the phrase ‘most Boeing 737s.’ The reason why I have said that was because there are 737s with tiller on the right side as well. It is a customer option. If the airlines want it, they can pay Boeing a little extra money and they will put in a right tiller. When the 737 came out, back in the late 60s, it was always the captain that taxied the aircraft. Those were pre-CRM (Crew resource management) days where the captains ruled with an iron fist. So, first officers taxiing the aircraft was out of the question.
These days, things are a lot more different. The captain is still the boss, but airlines take a lot of effort in ensuring that they do not have a rogue captain in their ranks. Allowing first officer’s to taxi the aircraft is a part of it. Giving such level of control to the first officer means that he/ she will be less afraid to make comments on captain’s actions if he or she does something wrong. The concept of Pilot flying (PF) and Pilot monitoring (PM) in the cockpit rather than captain and first officer means, that when the first officer is the PF, he is allowed to make some final decisions on how to fly the aircraft. The captain can always intervene if he feels something is not safe. At least that is what a good captain will do. There are also anonymous reporting mechanisms placed in by airlines, so that you can report it to the safety department, if someone is being too much of a jerk.
A Boeing 737 with a tiller on the right side.
Now, even if the aircraft is equipped with two tillers as a factory option, as found in all Airbus aircraft, the airlines can still enforce captain only taxi. Many airlines still have this rule in place. In some airlines, the first officers can taxi only when they gain a certain amount of experience on the aircraft. Once they gain that level of experience they are trained on the correct techniques of taxi in a full motion simulator before they are allowed to taxi in the real aircraft.