At the times a bus route would seldom used the Finch Ave bus would not be crammed.
Someone doesn't ride many suburban bus routes...
One example: the 42A. Maybe one or two people will be on it east of Victoria Park. Often, just the driver. And this isn't 10:30pm, when the Steeles East and Finch East buses are still leaving people behind at Finch station, this would be at, like, 7pm. They keep boosting service on routes like Steeles East because people were getting left behind at Finch station well into the night, though I believe service has finally caught up the 'acceptable level of crowding' seen on other routes.
There's dozens of cases of poor performing routes or branches that are chicken/egg scenarios - ridership is low because service is bad and service is bad because ridership is low, but only some cases will be improved by improving service first. The 42A will probably never have good ridership, no matter what arbitrary number you're using to define good, because there's so many other options for people in the area (Steeles, Finch, and a N/S bus route every 800 metres). Maybe they should run the 42A to Morningside Heights, but while that would increase the ridership, it would also increase the route cost.
"Essential" to the few people who use these routes/branches means little more than a willingness to wait around for them longer at a subway station in exchange for a transfer-free ride with less walking. Cutting them might mean adding a 200m walk, or a transfer from the Finch bus to the Warden or McCowan bus, etc. They're not denying someone insulin or shutting off the power and water in an apartment building. When surface routes are as good as they are in this city, it's no wonder some people see them basically as luxuries. Several times on the 42A, everyone but me has emptied out by Victoria Park or Warden and the driver has asked me where I'm getting off and then sped there...the quicker everyone's off, the more time he gets to rest at the end of the line. That's not essential service.
There isn't just the issue of freeing up a bus to use elsewhere when thinking about "resources," there's dollar and manpower issues to consider. An empty bus at 10pm probably runs full at 5pm, so we'd need to buy another bus to run another bus at 5pm, but the driver's time and pay can be moved from 10pm to 5pm.