I think I was about to report the same problem, although I noticed that street names do appear if you zoom enough. I'm attaching an edited screenshot to show the problem (I messed up the crop - the arrows supposed to show street names that do appear).
What I find esp. strange is that sometimes when looking at parallel streets with the same length and width only some of the street names appear.
I'd like to add that I also found this behavior on other maps (Google, Waze, even from the previous OSM screenshot I can't tell the names of streets between S Stevens and S Tyler, or between S 9th and S 10th...) but they don't have a feedback forum 🙂 This suggests that this is a problem with some common algorithm used for placing labels.
