Why It Is Not Possible to Make a Profitable Manga Subscription Service

The entire manga industry has a revenue of about $100 million per year in the
west. In order to compete with existing platforms, you would need a low
commision (patreon has a 5% commision, for example). So that would give you a
best-possible scenario of $5 million in revenue per year. If you do a really
good job, you might get a 5% market share, and earn $250k annually. You would
need a team of programmers and marketers to accomplish this as well as money
spent on promotions. This would eat up most if not all of your costs. Consider
that a single programmer in the industry costs $60-120k annually to employ. You
would need to hire people before even making any money, then afterwards to
maintain the system. The numbers just don't work out.

If you were a person capable of doing everything required to build and maintain 
the system all yourself, you would be able to make more money doing something
else or do something fun instead.

You have to go to a less sexy industry if you want to actually make a profit
because lots of people want to come up with the next great startup with the
first thing that comes to mind. Business is all about doing the work that
someone is willing to pay you to do. Garbage men make a high salary throughout
the world, for example. All a manga subscriptions would do is add extra steps
to giving the artist money, generating more work in the process.