Because that's how I made it!
:P
Seriously, the TB-23 and TB-29 are "Thin-Line Arrays" and the TB-16 is a "Thick-Line Array".
The same acoustic properties that give them greater sensitivity, also make them more suseptable to wash-out due to flow noise.
People who are actually schooled in sonar properties can probably give a better answer, but this is how I understand it.