I think it's a combination of a couple things. First, no big new splash this offseason that gives your typical fan something to be excited about. Yea, to those of us that are obsessed, there's excitement for Lazor's offense and the receiving corp. We know things have changed (hopefully for the better) on offense. Reasons for optimism: 1) Gibson, we know what we have now, from his mid season form last year, instead of just a FA that we are hopeful for. 2) Matthews, we know what he did last year, filling in respectfully after Gibson, you can't ask for much more as your #4/5 WR, last year it was a battle between him and Binns until Binns went down. 3) Clay, last year we thought we were screwed at TE after Keller went down. 4) the fact the Tannehill has 5-7 legitimate receiving weapons (Wallace, Hartline, Gibson, Clay, Matthews, Landry, and Moreno). For the typical fan though, they just see Moreno and Landry. They probably expect the same team as last year, with little/no improvements.
The other reason I think you see less excitement... Is because even given everything above, us die hards have this list EVERY year.... And Murphy's Law seems to apply to the Miami Dolphins better than anything/anybody else on this planet. I tell myself every year that I'm done getting excited. Last year I kept my excitement down some, until we started winning right out of the gate. I got pumped and what do you know, a train wreck.
For us though, it's hard to hide the excitement when we read every little possibility about why this team and this year is different. Ahhh, August.... The best time to be a Dolphins fan...