“My experience is companies do not anticipate that the cost of monitoring an application can easily exceed the cost of hosting the application even for simple applications.”
Logs start as print statements and end up as the customer service tool, the audit trail and the business intelligence source of truth. 99.9999% of them are never read, and they sit in object storage forever. Prometheus is built for one server, so scaling it means Cortex or Thanos and a pile of new services to babysit. The observability vendors make money on volume, so nobody sells you fewer logs.