Many creationists and other apologists both have and (usually implicitly) give a picture of science (especially those branches of science that they hate) as it being just a bunch of deluded people waving their hands and coming up with wild speculation and everybody else just believing what they say, without much question, just because they like it. A bit like some guy somewhere just one day comes up with a wild idea like "hey, whales and hippopotamuses look slightly alike, so maybe they are closely related" and everybody else is just like "yeah, that must be it; let's put that into the books!"
When you hear some of these creationists talk about science, they clearly paint this kind of picture. Even though this is outright ridiculous, they still get away with it, at least with their typical creationist audience, who see no problem in it. But why?
The major problem (dictated by practicality) is that the vast amount of work that goes into developing scientific hypotheses is hidden from the public. Not hidden as in it being intentionally secret, but in the sense that the public is never really exposed to all this work because it's not especially front page news.
Usually quite a lot of research and testing goes on behind these hypotheses. People work on them and write papers that are then peer-reviewed and tested by others. Other scientists may spot flaws or deficiencies in the methods used, and these may then be corrected or elaborated in further detail. Sometimes the conclusion of the research might be wrong, but it springs new better hypotheses (in other words, the original hypothesis works as an inspiration for other, better hypotheses.) Many of these hypotheses may have years and years of hard work behind them, made by dozens if not even hundreds of experts on their respective fields of research. The scientific method tries to ensure that flaws are spotted and eliminated, and that only the most accurate information is left.
What ends up in textbooks and scientific journals is, however, only the conclusions, because that's what's most interesting and important about it. The vast amount of work that went into developing that result is usually not conveyed at all. Thus it's easy for creationists to ignore the very existence of that work, and just imply that the result was pulled out from thin air.
The work itself is in no way a secret, of course, but getting and understanding it requires a lot of work. References would need to be followed, the papers being referenced be read, the papers that they reference have to be read as well, and so on, and all this has to be backed up by actual knowledge of the subject (which in itself may require years of study.) For a regular layperson it could well require years of hard study and work to fully understand the research behind the result, which is why this is so seldom done, and nobody even expects for the average person to do that, which is why only the conclusion is presented in a simplified manner so that the average person can understand the gist of it.
Creationists are extremely (and willfully) ignorant about this, and abuse the ignorance of others to advance their agenda. Even if you try to explain the amount of work that goes to develop these results, they just ignore it outright. It's pure intellectual dishonesty.