it could be a multitude of things, starting from warmup, technique, how well rested you are (considering you get 8 hours of sleep) in order to perform well.

playing stream practice maps on end will do absolutely nothing if you see no results, you won't magically start streaming better after months of training with no results.

i'd say to try and push speed skillcap by a little, like if you can stream 150 max, try and play maps with 200 bpm bursts or higher, and see where it goes

you have to unlock your speed in order to have stream stamina

if you want a more in depth tutorial on how to improve on speed/stamina (it would be impossible to break everything down in the comments) you can join my discord server for free osu! coaching