Because the other carriers don't use those as their primary bands nor have them deployed on every single site in the same way Sprint does for Band 41. Not to mention Band 30 and Band 66 still have farther reach than Band 41. Also Band 46 is deployed in very few places as a hotspot type of solution.
When you're on Band 41, you're on Band 41 alone. When you are on Band 30 or Band 66, you tend to be carrier aggregated with another band that has better propagation characteristics.
Where are you in NYC that you roam a lot? In the past 3 years I've used 0MB of roaming data. It's also important to note that Sprint's Sensorly map is skewed because of Band 41. Because of Band 41, Sprint's average signal strength will always seem lower than other carriers in the NYC even if Sprint's speeds are faster.
Sprint definitely needs it in NYC. I roam a lot. Look on Sensorly, which Sprint uses as reference, there are quite a few areas that are low in signal. Including in but not limited to Manhattan, without mentioning towers with signal but no service all over the city.
I personally one of Sprint's numerous mistakes in the past was in not prioritizing the tops markets. T-Mobile is not great outside of cities to this day, but few of it's customers know that.
On the same note
People pay for cell phones and service on other carriers for a reason.
If it is really important to you or anybody else Sprint, under normal circumstances, is not the best choice. On that note, I have a S9+ from Samsung which I configured to use "Calling Plus". It is a nice feature to have when I am not roaming in NYC, as I often do. I have been able to try T-Mobile roaming, and it works very well. I look forward to it being more wide spread.