Why hasn't anyone proposed a delta loop on a fishing rod yet?
It isn't expensive enough to be that good?
Because some people don't think beyond commercial
antennas and their marketing claims?
Full wave loops can be great antennas, and can be
installed in many different configurations. The shape
can be modified to match various impedances, from
less than 50 ohms to almost 300 ohms.
But while a traditional loop has a little bit of gain over
a dipole in free space, over practical ground the situation
gets complicated quickly. For a horizontally polarized
loop, a dipole or inverted vee hanging off the same
support may give a bit more gain at low angles, because
the average height of the antenna is greater. (The
bottom wire of the loop, being at a lower height,
doesn't contribute as much low angle radiation.)
For vertical polarization (which is what I presume your
loop is attempting to achieve by feeding it in a bottom
corner), performance is greatly dependent on the local
ground conditions. They are great over salt water, and
should work pretty well in much of the Midwest where
soils tend to have high conductivity. Here in Oregon,
where most of our soils are volcanic with poor
conductivity, vertical polarization at low heights doesn't
work as well.
But there is another factor that has been touched on:
what distance the antenna is intended to cover.
For really local coverage (out to 30 km / 20 miles or so),
height is more important, as the propagation is usually
via a direct wave, as is typical on VHF. This a low vertical
isn't going to work as well. In that case, you would want
a taller fishing pole. But for ionospheric propagation, that
isn't as much of an issue, and the low vertically polarized
loop can work quite well.