Why would he get weighed or timed outside of his friendly neighborhood Alabama Pro-Day? The guy is gonna come in at 165 lbs. and that's gonna scare GM's. His speed is already considered elite, so why take a chance on measuring it and being viewed as less elite? Wait until you've got the best possible situation. There is no Combine and he's not seen as ducking measurements because the Senior Bowl is lucky he is even attending. That's not a typical stop for the top 15 guys. IMHO, he desperately wants to be chosen #3 overall so wants to take the opportunity to hobnob with the Dolphins, because realistically, #3 is the absolute highest he has a chance of being selected. Plus he already has a good relationship with Tua, and I'm sure he wants to let the Dolphins know it an extra 50 or so times during the week.
Many people claim that the practices are the most important part of the Senior Bowl week, but there are also a lot of people saying the interviews are the most important part. By showing up and giving face time (the expression--not the copycat name used for the iphone app) to the Dolphins and making himself available to the GM's of all teams, he is probably getting from the Senior Bowl the absolute best parts for him he would have gotten from the Combine. Smart move on Smith's part.
Also, kids NOT doing what Davonta Smith is doing are missing the boat. GM's need to gain a level of confidence with high picks, and asking them questions on the spot helps allay their worst fears of drafting a bust. More prospects should be doing this in a year without a Combine. It shows courage and a competitive nature, which all GM's love.