Because that already exists… (granted, this is being used for a different purpose)

The red line is to mimic the red line you will see in Slack that denotes new messages are below it (in Slack), but in Discourse, it denotes, new messages are above it.
Even in Slack, that blue bar rarely appears for me unless I’m gone for hours/days, as there is rarely enough messages for it to stay shown. The red line though is always there, letting me pick up where I left off.