Increase in home prices/hot housing market in a suburb doesn't necessarily mean population growth. Due to declining household sizes, if a city isn't adding a good amount of housing units, it probably won't be growing, unless it is getting younger and attracting more young families. A population decrease doesn't necessarily mean an area is unhealthy or undesirable (although growth is obviously better).
Average household size continues to decline in the US. In 2016, it was estimated at 2.53, down from 3.3 in 1966 and 2.59 in 2000. Average household size in STL in 2000 (I'm not finding newer data) was 2.52, lower than the national average for metro areas of 2.61. In Wesbster Groves average household size was even lower at 2.39.
Looking at trends in median age since 2000, I think it is likely that household size in metro STL is dropping faster than the national average. Source: http://www.demographia.com/db-metroage.pdf
In 2013, average age in metro STL was 38.6 years, ranking 40th out of 52 largest metros. That was an increase of 2.5 years since 2000, greater than the national average increase of 2.3. So the St. Louis metro has an old population that is getting older, which means less kids and smaller household size.





