Do you happen to know why there's no plural form for the borrowed nouns ending in "o", like "radio"? Russian treats these words as neuter, which usually replaces the "o" with an "a" to form the plural (e.g. window), why doesn't it do it here?
But it's probably because of a declension choosing process which I described. Take "ра́дио", for example - it has this "ио" thing in the ending that is really not typical to Russian, so it made people think "hey, this word is weird, we probably shouldn't touch it when speaking", and since a lot of people thought this way, this became codified.
Now, some other loanwords are not that weird, for example "пальто́" - it's not that different from "окно́", or "весло́", or "ремесло́", and in fact, rarely people do decline it, like "пальта́", "у меня есть два пальта́", "у меня есть пятеро па́льт" - but it's rare, and "officially", it also has no declensions, probably to make things simpler.
