I have been thinking about it a lot, I don't think simple bigotry is a reason , it is something more fundamental. I am going to analyze this phenomenon with dialectical materialism, instead of using plain Marxist class analysis, I want to use dialectical materialism. I don't think a simple class analysis will ever properly cover this topic, plain class analysis focuses a lot on waged labour, it doesn't focus on the whole class society. I am gonna use Silvia Federici's criticism of Marx and well here so with that let's start.

First Marx talks about beginning of capitalism with primitive accumulation, for Marx this is about enclosure of commons and pushing previous peasantry into proletarian work, however for me this also means subjucating the things which weren't in the logic of markets to its logic, markets did exist in feudal times but they were secondary capitalism brings a point where production for market, the commodity production being the primary form of production. This means things like rights of disabled people are now question of whether they are useful to the market, previously existence of disabled people was neutral, they could do anything which was in capability, but now with factories being the place of production, if someone couldn't work in factory they were a 'burden' which eventually leads to the divisions of labour across the dispossed classes, we all are dispossed, we don't own any private property, able-bodied or not we all labour for our keep but the system interacts with us differently the able-bodied cishet man is the ideal worker, he is rewarded the most, then there are people who are engaged with half the wages or no wages in case of many immigrant domestic workers. Marx on the whole discussed the able-bodied cishet worker and that person is still the revolutionary subject today, we are reduced to objects of history along with majority of femme presenting people.

Secondly, Marx talks about capitalism as a progressive force something that brings progress, but I think that's because Marx considers the start of it with industrial revolution. I market he start of capitalism after discover of Americas, the start slave trade and genocide became the characteristics start to form here even if the capitalists haven't captured the power yet.amd feudal lords still rule the land. If we look at it this way, we can see instead of progressing towards something great, class is essentially decaying into less and less humane forms, for disabled people this means their existence now is reduced to cold mechanical logic of capitalism, until now they were allowed to exist, life wasn't a utopia or amazing but it wasn't bad either, it was life but now the project is to kick out disabled from the society as it became less and less humane. If we see it from the four stages of development talked about by Marx himself them we see it, first primitive communism was a place where classes didn't exist and humans lived a very different life, disabled people lived without classes, then slave society came and now the disabled were ostensibly pushed into a separate life from able bodied, then feudalism came and under single religious bodied disabled people were forced into private lives, with advent of capitalism now there's an active genocide of disabled going on.

Now thirdly, I want to merge these two points, this shows us that the reason most leftists don't keep disabled people and other dispossed classes as a class of workers in the center with other workers is because they are still stuck in analysis of Marx and Engels withe everything they got right and everything they got wrong, some read Lenin so they have better analysis of imperialism, some further read Mao so they have understanding of self criticism as well however in the end, their analysis also lack the things which the figures they read lacked knowledge. A good framework understands its own limits and by subsuming everything to logic of worker-capitalist contradiction, it becomes reductionist and leaves out the disabled people, and reproductive work of women.