How come women on the same dosages of steroids, with the same training experience, on the same programs, with the same bodyweight or even heavier by 30 lbs, as men on steroids are still considerably weaker, for example female competitive powerlifters, olympic weightlifters?
Because all other things are certainly not equal. The cow isn't a sphere, it is a cow.
Testosterone is critical, absolutely. However, it is more of a limiting factor than a dominant directly causal one. The male and female hormone systems are different in more than just T levels, and these additional hormones such as HGH, IGF, and others play a significant role as well.
Part of your question also stems from a societally induced belief that steroids simply make you big. They do not. Going above your body's natural growth limits may require steroids, but it will also require much more in terms of other bio-chemcial regimens and will have to be different for the sexes due to the underlying structural differences.
Thus putting a man and a woman on the same regimen will not produce the same results. For that matter, you can put two "near identical" men on the exact same regimen and not get the same end result. Other factors such as microbiome, individual normal shifts, and even mental factors throw a monkey wrench in the basic premise.
Finally, the changes necessary for the stronger muscles happen much earlier in life. Adding steroids or testosterone after physical maturity can not retroactively build the body for the higher load of activities such as powerlifting. Hypothetically it may be possible to produce a female with the same makeup by applying drastic hormone and strength training at a very early age but it would be a dubious proposal and certainly not one I'd expect to ever be done.
All of this doesn't mean an individual woman can not be stronger than an individual man. It simply means that the strongest male powerlifter will be capable of lifting heavier than the strongest female powerlifter - even (or especially) with the same regimen.
Other factors might include anthropomorphic differences (limb length, bone size and density, etc.) and also the crucial fact that the men in your comparison have been training for multiple years with those hormonal levels, which accounts for a superior lean mass and thus superior strength. Female competitive powerlifters or weightlifters or bodybuilders are much, much stronger than the average (and even slightly above average) gym goer because they have spent more time training in an anabolic state than them (despite their sex difference). I'd recommend taking a look at the international rankings in powerliftingwatch.com for anyone who doesn't think that is the case.
The explanation for this is because men naturally have higher levels of testosterone. This is because men have hormones that they possess in which people of the opposite gender likely would not. On average, a man usually has 20 times as much testosterone in him than a woman, no joke. This is why you will probably wonder why the majority of females at your gym are only lifting 5 or 10 pound dumbbells while you are pumping out a 180-Ib lift on the bench press. This isn't to say women cannot possibly be strong, it is just more of a struggle for them than men, and if a man and woman trained equally the man would probably bulk more because of his hormonal composition and levels of testosterone.