Why does Nautilus have such high mana costs compared to Sejauni?

cuz sejuani has tits

Nautilus is an old champ and hasn't received a rework yet.

Based on the PBE trend they are tuning Naut slowly into something better as they look at his ratios, cd's and costs. So instead of dropping a massive change on him and swinging him too far, they are easing into it. Realistically though, Naut doesn't have anything his kit that makes me want him more than Sejuani in a game.

Once you factor in their base mana and mana regen it's not that far off. Granted Sej has better mana usage early (Naut only starts with 284). But it was only a few months ago Sej got the mana buffs. So hopefully we'll see some changes for Naut soon.

That Anchor of his weighs him down a lot.