Why are these towns not growing?

[Argus]

Maybe also because you don't play as the system expects and you only use one type of vehicle. Where the game expects variability, only trains run.

[PikkaBird]

The town growth algorithm doesn't care what kind of vehicles you use, where they go, or what they carry; what percentage of the town's passengers or mail were transported, what any station's rating are, or what any company's local authority rating is; or anything else.

The only things that effect or affect town growth are:

• Between one and five stations located inside the town (ie, within a town zone), at which something has been picked up or dropped off in the last 50 days.
• Whether town expansion has been funded in the local authority window (temporary boost equivalent to ~ two stations).
• Whether the town is a "city" or not (increases the growth rate, but only if the town is already growing because of one of the above).
• Whether the town has received food/water, for towns above the snowline or in the desert (binary on/off, how much food and water don't matter).
• Whether a gamescript has turned town growth on or off (binary on/off).

In OP's case, the problem is probably that those stations are too far outside the town to be in zone 0 (the station location is where the name sign is - it's not testing every tile or whether buildings are in the catchment). Even if the stations are moved closer, with only one station and a slow daylength, the towns aren't going to grow very fast.

[jfs]

In addition to PikkaBird's post above, the generally most effective to make a town grow is to place two bus stops inside the town, right next to houses, and make a bus run between them. That gives constant transport activity inside the town, meaning that you will definitely fulfil the first point on Pikka's list. (Except if the town is so small that it doesn't generate enough passengers, or cannot accept passengers.)

[Argus]

Yes, it always helps