Because 4's board design and items are blech. 1 has really good boards (that are prime for dicking over everyone else) on top of being able to turn on random dice blocks like warp blocks, 1-3 dice blocks, 8-10, minus and plus blocks, boo/koopa/bowser block, etc etc. More RNG on top of the already punishing stuff 1 does is great.
Truth. MP4 fans need to go back and remember those ugly boards and slow movement. It's not bad, but no series highlight.