This is a long-standing shortcoming with United, made worse by the fact that United's union rules limit what the outsourced agents can do (even beyond the limitations of their training).

The union probably figured it could force UA to keep CS staffing halfway robust at check-in if it negotiated an agreement that only actual UA employees could perform certain functions. UA laughed, said, "Watch this," and dispatched a bunch of outsourced folks to stand around while customers gave up and tried to check themselves in or waited until a real agent materialized after 2-5-15 minutes.

This problem has existed for at least the greater part of a decade, at least at certain UA hubs. Ironically, it doesn't seem to be nearly as much of a problem at non-hubs, where I've never had a problem finding an actual UA agent at check-in. One possibility is that, at non-hubs, most travel issues requiring an agent (other than last-minute issues at the gate) are handled at check-in, whereas, at a hub, most passengers are connecting, so their problems are handled by customer-service desks airside.

I guess United has concluded that its customers won't punish it for skimping on staffing. Given how much UA focuses on business travelers, who rarely check a bag and thus tend to check in online, I guess they may be right. But, having split my travel between UA and DL, the difference in staffing by fully equipped agents at check-in is stark.