The main problem is there are not enough drivers. Every driver we had in January told us the same thing. They can add as many cars as they want but without drivers it wont make a difference. It also will not be as hard to get one once the popularity dies down either because truthfully, how often did you ever see Uber or Lyft or even taxis lined up at any of the Parks at closing. 2 or 3 maybe, but not 10 -15 of them. Most people are not going to pay $25 Plus tip when they can get a free bus ride back to their resort.
Not to sound like a scrooge, but you do realize that with the Minnie Van service, tipping is completely unnecessary since the cast members are paid hourly but you are welcome if you would like. Also, using the Minnie Vans for ECV's might be easier than loading and unloading with the bus service. Also, for parents with young kids, the car seats are included in the price compared to Uber or a taxi.
It is a convenience factor and I personal see a lot of people continuing with the service because they hate waiting a long time for the bus service or hate waiting for the loading and unloading of ECV's.
Only time will tell how the public will respond once the "newness" wears off.
Prior: Offsite most every other years from 1972 - 2000
Most recent: Offsite 2001 & 2003 / ASM 2006 / Offsite 2009 / Poly 2011 / POR 2013 / CR 2014 / GF 2015 / Offsite 2017