Tight ends are surprisingly risky investments in that so few true impact players become available in free agency. The low supply tends to raise the price beyond where demand would otherwise set the bar.
The highest-paid free-agent tight ends the past few years have ended up being bad investments and in most cases no longer are with the teams that signed them.
To wit: Think about Jared Cook ($16 million guaranteed in 2013), Brandon Pettigrew ($8 million guaranteed in 2014), Julius Thomas ($24 million guaranteed in 2015), Dwayne Allen ($16 million guaranteed in 2016) and Martellus Bennett ($6.