If He wanted us to do the chumras, THEY would have been the halacha m’Sinai.
Many of the chumras are just that; they were proper halacha but due to economic and social hardship in Europe and the Eastern lands as well as the travails of the early emigration to the US, it was impossible to keep halacha on a proper level. Now, with economic prosperity and social freedom everywhere Jews live except Iran (and now Venezuela), we enjoy our freedom as Hashem wants us to, by giving up the phony yoke of social correctness in favor of ol malchus Shamayim. However, since there are those sincere Yidden who still live in the old times and do not realize why we have our freedom, the halachic corrections are mistakenly called chumras instead of what they are – corrections or hachzoros atoro leyoishno.
On the other hand, heterim and kulas are not meant for everyday living. They are meant for situations such as travel, interaction with secular relatives, baalei tshuva at various times in their personal development, physical and psychological limitations and illnesses L”A etc.
If the first immigrants to the US had been able to hold on to Yiddishkeit instead of kosher and Shabbos keeping Yidden having become a minority very quickly, we probably would have had cholov Yisroel, pas Yisroel, and glatt as the standard in the United States as the CY standard would have developed in 1880 and not 1955 so that the large firms would have had to have allowed mashgichim for C”Y (which is not hard anymore and one day the present situation will be fixed when a major firm goes C”Y and brings costs down).