Basically, telco is a fee for carriage service. You pay for transport on some network that they build: cellular, fiber, etc. They figure out what to charge you based on historical models of what you used the transport for.
In the days when all that you transmitted were telephone calls, this was easy. Then people started sending IP packets and it got a little harder, but ok, the telcos would just charge a per byte fee. The money was in charging to carry your phone calls and SMSes anyway.
Then the smartphone exploded and suddenly consumers did not give a hoot about phone calls. The sole reason to have a cellphone plan was to get data. The telcos had to expand the network capacity by several orders of magnitude for a customer base that had absolutely no desire to pay by the byte. This blew up their model. Moreover, telcos saw that people were paying $$ every month to folks like netflix, watching video on their phones, chewing up network bandwidth, and the telcos werent getting any piece of that action. Hence the whole net neutrality thing.
The aim isnt that telcos have app stores. They know they cant compete with that. The holy grail is that a telco finds some use of the network that commands a premium price that users will accept. Verizon trades on having the best-est network. AT&T tries to bundle, eg HBO. Tmo goes after the younger customers with discounts.
Now 5G is here and telcos are desperately, desperately trying to find uses for it that cant be satisified by the existing network and biz models. Will they succeed? I wish I knew.