Since underneath it's a (T, bool) pair, it will add at most 7 bytes to the size of the object, meaning seqs of Option[T] would be a lot bigger (stuff like that compounds if you're not careful) and because of less elements fitting in a cache line, decreases performance. Performance may be worse for other reasons as well.
It also changes the "ergonomics" of the libraries using them, meaning you are forced to pass and unpack options everywhere. And last thing, which is due to programmer's oversight, it adds unneeded conditions. It's hard for me to explain but you can infer the existence of a value from another related one, it complicates code, rather than make it easier to reason with. Of course that's my personal opinion, other people may love options for their own reasons.
