Well apparently in their mind the interior OL was not that huge a need. They had confidence in Allen, Corbett, Edwards, etc... I remember McVay pointing out that their top 9 ir 10 OL were all coming back and they felt there was no need to replace anyone in that group.
I mean they did win the SB afterall.
Now, Tutu may have been a reach, but McVay apparently felt speed at the WR position was a huge need ans not currently on that roster at that point. So they took a shit with him.
And far as taking OL high, there are probably more 1st round busts at OL than any other position. So it's not a slam dunk.