Catch 'em, Ketchum

Reading about the Virginia Saltmarsh Mallow got me wondering how the word 'Mallow' is pronounced. My instinct is to say m[æ]llow, but what about marshm[ɛ]llow? Come to think of it, why is marshmallow pronounced with the DRESS [ɛ] vowel in American English? UK English seems to roundly prefer marshm[æ]llow, as to rhyme with 'hallow.' The predominant American form is, I think, marshmellow. But where did this pronunciation come from?

Another word with an 'a' spelling but an 'e' pronunciation is 'any.' Unlike 'marshmallow,' I can't actually think of any case of someone pronouncing 'any' like [æ]ni. 'Many' used to be pronounced with an [æ] sound, and a relic of this is the word 'manifold,' which comes from 'many' and has an [æ] sound. Under the influence of 'any,' it came to be pronounced as 'menny.' Why 'any' came to be pronounced with the [ɛ] in the first place is unclear, too.

Here is another one - a common pronunciation for 'catch' in American English is c[ɛ]tch. This one is common enough that it formed the basis of a pun name in a popular show. The Pokemon tagline in the 2000s was "Gotta Catch 'Em All." In that vein, the main character was named Ash Ketchum - as in Ash "Catch 'em."

I'm not sure how [æ] became raised in these cases. Any thoughts?