In simple words, when [ɛ] is lowered, it becomes [æ]. It's what's happening in the examples the OP has given. There are a few factors that are responsible for this shift. Two of them are:
Northern Cities Vowel Shift
[ɛ] is an open-mid vowel while [æ] is a near-low vowel. One of the reason that accounts for the lowering of [ɛ] to [æ] is the 'Northern Cities Shift' from the Inland North dialect of the United States (as Legatrix pointed out in their answer). It's a chain shift of vowels through which some vowels have changed their positions in Inland North dialect region.
California Vowel Shift
Another factor is the 'California Vowel Shift' through which some vowels have been shifted in Californian and other Western American accents. So you're hearing them correctly.
California Vowel Shift: [...] /ɛ/ is pulled towards [æ] (wreck and kettle are sounding more like rack and cattle), /æ/ is pulled towards [ɑ], and /ɑ/ towards [ɒ] (cot and stock are sounding more like caught and stalk).
Here's the vowel chart of California vowel shift (CVS) where [ɛ] is indeed lowered to [æ]:
This paper has summarised CVS as follows [modified]:
- /ɪ/ fronting before nasals (pin-pen merger)
- /ɛ/ backing and lowering
- /æ/ raising to /eɪ/ before nasals and lowering and backing elsewhere
- /ʌ ʊ u o/ fronting
- /ɑ/ and /ɔ/ are completely merged (cot-caught merger)
There are also other mergers such as the pin-pen merger, which is a merger of /ɛ/ and /ɪ/ before nasals ([m, n, ŋ]). The resulting vowel is usually raised. Homophones include pin-pen, meant-mint, tent-tint etc. It's found in Southern and Western US.
I'm not very well-versed in American accents, but from what I've read, these shifts occur in many American accents. Read the following papers for more details:
And this brilliant ELU answer by tchrist