I seem to have warped rotors! What's causing this? How can I prevent it?

I drive a 2004 Honda Accord 4cyl. Last October I replaced all of the brake rotors which I believe were original based on their drastic condition. The pads were replaced as well. I lubed the sliders and replaced the hardware as well. For a while they were perfect, but recently they are pulsing as if at least one of them is warped. There's no knocking noise, steering noise or any indication to me that there's a problem with CV joints or tie rods or anything like that. My last two cars were an 04 Accord which I bought new and drove almost 300k miles and an 07 Accord which I bought used and took to 200k miles. Both of these cars seemed to always develop the same problem as well. How can I remedy this and prevent it from happening? I'm not hard on my brakes since I drive a manual and do a lot of hwy miles. Any advice is much appreciated!

Rotor not aligned straight or wobbles causing uneven wear, could be so much as a piece of dirt under the rotor or rust not cleaned off evenly before placing rotor on, something is not straight… If you don't have a dial indicator fix a rod near the rotor and turn the rotor so you can see if it wobbles (with new rotors of course)

If you bought cheap brake pads they are too hard and can cause rotor warpage. Did you replace the brake hardware? When doing a brake job the right way you remove the hardware that the brake pads ride on in the caliper brackets and wire brush an file the rust build up off of the brackets so that the brake pads move freely. If you don't do that the pads won't release completely and that heats the rotors and causes them to warp.
Brake rotors should be able to be warrantied for 1 year or 12,000 miles. That's why you buy them from an auto parts store rather than on line.

What seems is not what you think it is. Take a pencil with a rubber on the end(erasure). Now hold the pencil by the sharpened end in your fingers and put the erasure on the clean desk so the pencil is at a 60degree angle and push the pencil forward. The erasure will bounce as it grabs and lets go. You brake pads are doing the same thing, they are sliding and catching at the same time. You get this pulsation. This is due to the types of materials they use in those pads. Like bits of rubber in it.
When I get brake shoes, I get metallic shoes which are harder. They tend not to do that kind of catching.
Or the rotors are glazed to a mirror like finish. Let a mechanic look. They may need to turn the rotors(take off a thin layer of metal so the rotors are more like sandpaper) and take any warpage out(which I do not believe is the problem, for to warp a rotor TAKES A LOT to do that kind of damage).
Mine is 07 as well, and I do not have that kind of problem yet.