Why are ports on top? Because it's a design holdover from full towers that used to sit either on the floor or in a cubby next to the floor. Added with multiple optical bays, floppy bays etc that ate up higher access (the bottom being all fan space, that left the top as the most viable spot. It's also more practical in the sense that a USB plug sticking out the front of a case is definitely in a bad spot when ppl or animals go past, they get broke off quick.
Why TG? Why not. It's really no more of an insulator than giant plastic side panels or even the sheet metal sides used in more premium cases. It does allow for better visibility of the interior and is far less prone to scratching than acrylic. It also does not cloud over like acrylics can with age and heat.
Personally, a heavy case is a bonus to me, lightweight cases in a tower design on a desktop just feel flimsy and are prone to knock-overs by cats or ppl not watching where they are going. A solid, heavy case goes nowhere, no matter how hard you slam the vacuum into the desk.
There's been all kinds of pc's built in open air, even the ones designed to hang on the wall like a picture, just a little glass in front to protect from direct contact. They have one thing in common. The owners spend more time cleaning out the dust than they do gaming or using the pc. A case does a lot more than be a box designed to hold the components, it's also for protection of the components from outside abuse (like when the cat jumps up on the desk, or your 3 yr old discovers she can throw dolls) and they also protect the components from excessive, immediate dust. Pull the side panel off if you want to, just invest in multiple cans of compressed air, your cleaning regimen will go from every few months to every couple of days.