I don’t monitor HR much indoors, but it looks like you rose to a tempo pace for most of the workout and added a short Zone 5 effort at the end.
MPA drawdown only occurs when you spend enough time above TP. That can either be hovering above TP (not at TP) or spend longer intervals in yellow/orange or shorter spikes in red with minimal recovery in between (green/blue) to keep MPA down.
You lowered MPA to a point as difficulty and fatigue rose (shaded portion of the graph) but there was lots of time in green (below TP). IE, sweet spot/tempo territory. Challenging for sure, but not enough to continually drawdown MPA and trigger a BT. Had you done that (more orange/red) the graph may have looked more like this –
Let's See Some Recent BT's - #289 by Erph
Page through that thread and you’ll find various examples of MPA drawdown including some similar to yours but with enough efforts while fatigued to trigger a BT.
As @johnnybike and @Cyclingdoughboy mention your high PP/HIE is a factor. How often can you hit that maxP number outdoors when fresh?
You could experiment with your numbers by selecting the Advanced MPA tab for that activity, change any of the signature values and click Refresh. That will recast the chart. You don’t want to save the new signature, but you can use this method to play what-if scenarios. For example, what if TP was 10 pts higher.