Madara was just hot-headed and wanted to test Hashirama's regeneration abilties augmented/powered up by Sage mode.
There may be also other reasons why he charged at them head on:
1) He believed he won't give even them time to act with that speed
2) He was careless
3) He sensed a lot of people aka alliance army around when he attacked knowing that Tailed beasts won't use TBB.
Madara himself admited being careless due to these powers, before he got Rinnegan:
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^^ even if Madara used absorption power, which is much infferior to preta path absoprtion powers, Madara would be done for once there is more then once TBB shoot at him or Kurama tbb