Why does the end grain on my table look darker after staining?

End grain usually takes up more stain because the cut ends of the wood fibers absorb it readily. That can make the ends look darker than the long-grain surfaces, even when you use the same stain.

Uneven sanding or differences between boards can add to it. If the darker area continues into the face grain, it may be natural variation in the wood or uneven stain absorption rather than just the end grain.

For a more even result, test your finish on offcuts from the same boards first. Sand the end grain progressively and evenly, then try a stain conditioner or a thin washcoat to slow absorption. Those can reduce the contrast, though they may also make the overall color lighter.

If you like the darker ends, there is nothing wrong with leaving them as part of the wood's character. The exact finish is hard to identify from appearance alone, so I would test a few options before coating the whole table.