Re: the sound t ̬.
Why? Because people do it.
Here's my non-linguistics take:
Vowels are voiced. The difference between t and d is the voicing. If you don't stop voicing after the vowel and let it slide right into the next vowel, you change your t to a d along the way. If you have to "unvoice" for the next consonant, then your t remains a t.
The "oo" sound can actually like y+ew, so the second t sounds like a t before that y.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.