Because US citizens have the right to vote in federal elections, no matter where they live, and which set of federal officials (senators and US House district, and state electoral votes for President) you are voting for is chosen by your last US residence before moving, or if you’ve never lived in the US (like my child might), by where one of your US citizen parents last lived. It’s then up to that state whether you can also vote in state and local elections.

If you are a US citizen, even if you’ve never lived in the US (born to a US citizen parent), get on over to https://fvap.gov to get yourself registered and request your absentee ballot. Hurry up, because the deadline for most states is rather soon, and a lot of them still require the registration to happen via paper mail - plus, you need time for the ballot to get to you and for you to mail it back.

As long as the US is going to insist I report all my German income and accounts that I’ve already paid Germany’s well-collected taxes on, you’re darn right I should have the right to vote!

Because you're a citizen and you pay taxes.

It is possible to live somewhere for 9 months every year and yet those 3 months you're not there could be when voting happens.