i was looking at adjusting brakes on my triple axle trailer, so i noticed the front ,,,drives side,,, tire was SHOT!!!!!
all the other tires looked great.
why would just one tire be bald???
just a bad tire??

Axle and/or spindle is either bent or out of alignment.

no,,,,not that i can see
the wear on tire is even ,,i guess,,thread ,,then blad in center of tire..
7.60 x 16 tires 12 ply

some of those front tires get slid a lot in backing or tight turns, IDK angle or attitude of the trailer and pivot points can make a differnece

I concur with slightly out of alignment or your wheel bearing may be getting ready to implode and it is creating wobble. The sliding of a tire could make a difference when turning, but rarely will this make only 1 tire that noticeably different.

OR: If the center of the tire is bald? It is possible the tire is "ballooning" once heated up and is an indication the inner belts are separating. Here is a tire I had on one of my car trailers a while back. It ballooned, then lost the tread. I made it to the next exit (about 5 miles) and it was still holding air. Weird.... But tires will surprise us at times...

center wear is generally overinflated (extra PSI balloons tire and removes tire tread shoulders from contact patch)

Been there, exact same scenario on my toy hauler. Blew out the left rear (triple axle) which is just fore of my fuel station and 50 gallons of gasoline. I got REAL lucky on that one.

yea,,turning or backing tight places the tires are sliding...
but strange ,,,just the one tire.
i inflate tires to 45 psi,,they are a 12 ply trailer tire.
as to getting them hot,,the boat launch is 2 miles from my house or meijers prem gas 5 miles.

Invest in an infrared thermometer... very quick to determine issues before they are catastrophic.

All the tires are matching?

yes , tires are all matching
getting old now perchased in 2012
i have one of those heat guns