I know, I just get used to using the actual delete key when I'm using an external keyboard, so my muscle memory never kicks in fully to use fn+backspace.

That's what external keyboards are for.

I find the built-in style is fine for casual work, even typing documents, but for programming I love my delete key too much.

On the mini keyboard I find myself using ⌘X in place of Fn-Delete, it's a one-handed thing that's more convenient. If you have nothing in your paste buffer that's important it works out well.

I have a laptop which has all these keys though, in a 15" form factor. There's no reason Apple can't put these keys in (and they used to) - they just don't want to.

For whatever reason, Apple prefers to make a single keyboard for their laptops, regardless of the size. Even the 17" had the same keyboard.

Plenty of small laptops with a dedicated delete key. Don't see why Apple couldn't add one.

Probably because the overwhelming majority of people don't really care.

Those that care about a forward delete key are in the minority. They're also the type most likely to have some kind of highly personalized keyboard with very particular Cherry switches and keycaps.