Yes, that is curious. I wonder if anyone in Congress is asking the question. From the example of 1970, the law passed and Nixon signed it, even though he doubted it was constitutional. He turned out to be correct. The extension of the franchise to women —also via constitutional amendment.
1970 was different than to day in that the emotional logic ( know that’s an oxymoron) was if we could send 18 yo kids off to war, they should be able to vote. From that perspective, it does make sense.
Today’s reasoning for 16 year olds is purely to get brainwashed kids to vote demonrat. They do not have the maturity to have the slightest clue what they are being tricked into. Kids have a herd mentality, where if one jumps off a cliff because it’s cool, most of the others will too. Any kid that does not follow the herd is shunned.