I would suspect the culprit is the 10% bleach. After each use you are removing any surface oxidation that prevents significant buildup of rust on the tool. My wife thinks that every thing needs to be sterilized, Consequently I have to replace the toilet seats every couple of year because they are destroyed by the beach. Same with your tools.

If you are really fussy about cleaning your shovel, clean any dirt or mud clinging to the surface, and put it in the shed. Removing the clinging dirt will keep the shed clean.

The natural oils, minerals, etc in the soil put a coating on the tool that will keep the shovels from rusting.

The 10% bleach will never let the shovel develop the natural coating that will prevent the rust.

If it does get a little rust a couple of minute of use will remove it all and leave the tool bright and shiny

I seldom clean a tool that I use in the soil. If they get gummed up with mud I just let it dry bang it against a metal post to knock the dried mud loose, if that does not work I will scrap the dried mud off with a file or pocket knife. If I do have a rusty tool I will spray it with phosphoric acid. I am much more concerned about keeping the handles in good shape.

I tend to the other end of most of my tools, the wood end. I like wood hardener and pour some extra of it where the wood meets the metal. And hopefully I won't get any surprises next year, like rotten wood. I don't sharpen my shovels, maybe I should.

The easy thing is to bring the hoses in for the winter, a surprisingly large percentage of folks don't. The washers, and the hoses last longer.

I see no need to use bleach for tools.

I use bleach on garden shears and other clippers between plants so that I don't inadvertently transfer any diseases and such from one plant to the next. I'm not concerned about the shovels (that was just an example I'd heard of), I'm concerned about cutting tools and keeping blades sharp.

I would suspect that what ever is in your yard is all over your yard. So unless you have a large number of acres, there is no need to sterilize your tools. While I have never sterilized anything I used in the yard, I suspect there may be some minor benefit to sterilize if you have used them on a new plant.

However on a small yard if there is any disease in the new plant it will be transferred to all others in your yard. If you have a normal yard there are voles, moles, and several other underground animals, insects that move above ground and below ground. plus all of the birds and animals that populate the above ground areas of your yard. If the animals do not transmit the disease to the other plant the watering and wind will. So Sterilization of your tools wlll probably do nothing for the health of your plants

FWIW I've never cleaned or "lubed" the business end of garden tools. I do however dip shears/clippers in a weak bleach solution between plants when trimming tomatoes. Every couple of years I do "wet down" the wood handles with linseed oil and let dry. Pick a sunny day for this.

That was a good point Danelle brought up about not transferring problems between plants. One might think blights and such would be present all over the yard.

But tomato blights seem so spotty in my yard that I do everything I can to reduce them. I plant twenty tomato seedlings in May, and a month later three are burned up and the rest are fine. Since the neighbors trees shade most of back yard, I have to use a small area of the yard.