Here's what I had to do on my Kat earlier this year to get my brakes to work.
I removed the calipers from the bike, I cracked the bleed off valve & squeezed the caliper piston all the way down using channel locks, when the piston was at zero I tightened the bleeder valve. I did this to all my calipers. Once I reinstalled the calipers back on the bike I bleed them, I don't know why but this worked fast.
Unless you have a leak in your lines I would look at the master cylinder.
It might also be that you have to wait a few hours for the bubbles to rise out of the lines after you try bleeding them each time.
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