the irs doesnt need private keys or the seed to achieve their main objective; all the need is a list of addy you control. at that point they have all the info they need as they can then monitor those addys.
Imagine they had an 8yo seed which was used with coin control ever since it's been generated. Having the seed means knowing its entire history and, moreover, you now know all this history is of one single person's finance. It's their wet dream..