Vayikra 5 describes the offering required as a Chatat. This subcategory allows offerings of varying value, depending on what the guilty person can afford. Vayikra 5:11 reads
וְאִם־לֹא֩ תַשִּׂ֨יג יָד֜וֹ לִשְׁתֵּ֣י תֹרִ֗ים אוֹ֮ לִשְׁנֵ֣י בְנֵי־יוֹנָה֒ וְהֵבִ֨יא אֶת־קָרְבָּנ֜וֹ אֲשֶׁ֣ר חָטָ֗א עֲשִׂירִ֧ת הָאֵפָ֛ה סֹ֖לֶת לְחַטָּ֑את
And if his means do not suffice for two turtledoves or two pigeons, he shall bring as his offering for that of which he is guilty a tenth of an ephah of choice flour for a sin offering
It seems to be the case that some people cannot afford mammals or birds, so the text allows them to achieve atonement using a flour offering instead. This option, though, is not given for other offerings, and yet those same people would have the same financial limitation. Would they then not be allowed to atone for other sins or satisfy other sacrificial obligations?
In Vayikra 14:21, the text again discusses someone of limited means. One who can't afford 2 lambs (as per pasuk 10) can bring one lamb and 2 birds. But while the text acknowledges that someone might not have money, and includes the variable notion when making the offering, there is no option for "only flour" (at least to replace the animal part of the offering).
How does the poor person satisfy his various obligations if there is no "flour only" option and why doesn't the text offer the same option for the poor man as it does in those limited cases in perek 5 in other situations?