Mike Wright would argue otherwise. Certainly, it may not be as common, but it's not like it just doesn't happen at all.
Mike Wright was Chris Jones, if Jones develops. An undrafted role playing backup. As a role player, both he and Jones had some starts, but neither is/was a dominating player that wrecks other teams at the line of scrimmage.
Chris Jones has pass rush role playing skills
Did Mike develop into Vince Wilfork or anything like him? With Wilfork and Kelly both on the other side of the hill, we need a dominant replacement to go along with role players.
Ironically, Kelly is the exception to the rule, but if you count up the Pats draft picks spent on big bodies, from second round picks Marquise Hill and Ron Brace to dozens in lower rounds and free agents, you don't find one
dominant Tackle. Add the dozens of big guys on each team in the league and the rarity of a Tommy Kelly stands out more.
Lots of competent role playing tackles that just don't have the physical frame to carry the mass needed play every day. Different type. You need at least one physically dominant type, preferably two (or three if we went back to a 3-4. No coincidence we spent a precious fist on all three DT/DEs back then).
Siliga is more likely to end up on the Kyle Love end of the scale, but he at least has the body to be a mid level stalwart.
I don't think people appreciate what a freak Wilfork is if they expect someone to develop into him, or into Seymour, for that matter. That's the answer to the question why did they draft Brace high. the answer, he could possibly be a force if he was motivated. Armstead might have the size speed to develop and probably would have been a high pick without his weird medical history.
Belichick has said it himself, regarding his propensity for drafting these players in round 1, 'there are only so many athletic 300 lb + players in the world.' (paraphrase).
