If you assume that mapping services on a low-to-no bandwidth connection are important to them, they'll hear about it through word of mouth. Anything that solves a real problem will spread that way.
Contrapositively, we can conclude that mapping isn't much of a problem for these people.
The other problem with any map tile downloading is that it eats up their entire 3GB of transfer and their phone is dead before they even start. Catch-22.
My experience trying to get it to find a route to work just now involved finding my street name but not being able to enter my address, not being able to enter my workplace's exact address either, getting told to take an express train to a stop that I know it never stops at during peak hour, and searching in vain for a way to change the trip time. I bet it also can't handle delays, cancellations, or bus replacements.
Maybe it works better in your city? I notice you wrote "we can conclude that mapping isn't much of a problem for these people", but you could use the same evidence to conclude Osmand isn't much of a solution for their problem.
(I will note that I use it for hiking and it's very good for that, as it is for cycling.)
At that point, why would you use Google Maps at all? Osmand will do the same thing, and requires no connection.