Don't know if you can sand it but even if you could, you would run into aggregate (rocks) and would not get far.
I had the same problem in my pole barn. I took a circular saw with a masonry blade and cut out straight lines going in the direction you want the water to flow. the lines are 4 to 6 inches apart and only as deep as need be to get the water to flow out. you could mark them out with a chalk line so they are straight and spaced right.

You can have concrete ground down if you want.

Diamonds make short work of any aggregate.

It is not cheap, since the tooling does wear.

Be smarter to go to auto supply store & buy a snow brush, 1 I have is about 2 ft long & brush the snow off vehicle before parking it in garage. Messing with the floor may give you more problems! Grandma's broken hip, broken high heel etc. I sure wouldn't want a garage floor with dug out spaces if they go under the door then critters will be getting in. We always knocked snow off before putting vehicle away. We wanted to save the car's paint & garage floor. The brush in case they want to know what you are talking about besides being 2 ft long has a plastic scrapper at 1 end to get snow off windows, other end has a long skinny brush. The end bristles will wear off & then you just cut that end off & round it & use it until it needs it again. No sense getting new 1 every time the end needs trimming, i use them in sunny Ca. for everything so am harder on them here than in So. Dak. Have 2 & they are still going strong after almost 40 yrs. I'm sure they still make them as very practical. Maybe not as good quality as in the old days!!

You can rent a concrete grinder / scarifier (sp?) from any good equipment rental place. I had to do this a few years ago when the idiot concrete contractor decided to dump the rest excess concrete into my slab and just smooth it out. Center of slab was 7/8" higher than surrounding points (about 8ft out from that center point).

Grinding took a gay, in my case I actually removed more than 7/8" because the grinder leaves rough grooves that you'll then have to fill back in with a floor levelling agent. For garage use make sure you use a levelling agent that can withstand vehicle traffic and weight.

Renting of the grinder was something on the order of $60/day. Ran on 220V, but it came with a LONG cord so I was able to reach my 30A/220V dryer outlet and use it no problem.

This is a very messy project. You will get concrete dust everywhere. Move everything out of the garage and seal up anything you don't want to get dusty with plastic drop clothes and painter's tape or duct tape. You'll still find dust in places that were taped off, DO NOT use anything wet to clean the dust off... try and get the dry concrete dust up with shop vacs and swiffers first.

K