assalaamu `alaykum, raHmat Allah wa-barakaatuhu
In the Hebrew calendrical reckoning, there is a concept know as `ibbur (lit., "impregnation") whereby a month is added every so often in order to keep the Spring festivals in the Spring and the Winter festivals in the Winter, etc.
Why does the Hijri calendar continue indefinitely with Ramadan falling in all secular months eventually as it moves across the solar calendar year out of sync? Is there a reason for this? If so, what is it?