In Moscow - "В Москве", why "In Sochi" is still "В Сочи"?

Question

When you say "in Moscow" or any other city or place you change the ending - Москва, в Москве. Why you don't change ending for Sochi ?

Answer 1

In Russian language personal names and cities' names ending with "И" are exceptions and do not follow the cases. As well as some foreign names.

Answer 2

There are word endings that don't change in any case, particularly in Prepositional Case. Sochi is one of those words. Colorado, Idaho, Buffalo are all also places that don't change (as foreign words ending in 'o' don't ever change in Russian.) Hope this helps!