> plains and steppes – that is large expanses of semi-arid grasslands. The very nature of that terrain configuration produces fairly extreme seasonal temperature variations (that is, very hot summers and very cold winters) as well as extreme daily temperature variations (that is, hot days and cold nights) because such places are far from the large bodies of water and also don’t have tree-cover, both of which serve to moderate rapid temperature changes. [...] There’s no reason to suppose the Dothraki Sea would be any different: it sits at about the same latitude as King’s Landing so there is little reason to assume it would be warm all-year-round.
There are more reasons then just weather patterns estimated based on location and terrain for cloth to be less practical tho.
The same blog applies the same pedantry to clothing of other groups and to military aspects of different groups too. It is not like Dothraki were singled out in a blog that otherwise ignores clothing and practicality.