The Torah explicitly says that we may not eat blood because the blood is an essential element in effecting Kaparah (as explained in Vayikra 17:11 among other places):
כִּי נֶפֶשׁ הַבָּשָׂר בַּדָּם הִוא וַאֲנִי נְתַתִּיו לָכֶם עַל־הַמִּזְבֵּחַ לְכַפֵּר עַל־נַפְשֹׁתֵיכֶם כִּי־הַדָּם הוּא בַּנֶּפֶשׁ יְכַפֵּר׃ For the life of the flesh is in the blood, and I have assigned it to you for making expiation for your lives upon the altar; it is the blood, as life, that effects expiation.
But Vayikra 5:11 mentions that, for those who are too poor to afford even birds, one may bring a flour offering which will effect kaparah using parallel language in terms of the presentation and efficacy of the flour.
If that's the case, why isn't the same forbidding of consumption extended to flour, as it serves the same role as the blood in the sacrifice (or some part of it does). In the same way that the blood is the means by which an animal sacrifice is effective, something IN the flour, (not the action of sacrificing something of value) should be that same essence for kaparah and should be forbidden.
How are they different? Is there another reason for forbidding blood related to its being the seat of some life-force (נֶ֣פֶשׁ הַבָּשָׂר֮ בַּדָּ֣ם הִוא֒) which makes it distinct, and the utility of it in terms of sacrifice is not the reason? Is it a special rule for an unstated reason which we don't expand to similar cases because the specific rule does not include other things?