As a parent who has a child with a disability - it is expensive, time-consuming and stressful to get a child properly diagnosed and get appropriate accommodations. I find it highly doubtful that there are lots of scofflaws able to easily get accommodations who are now overrunning colleges and universities.
I do think there is more awareness of disability since the ADA passed in 1990 (yes we’ve only had the ADA for 35 years), and the stigma attached to getting tested/diagnosed has lessened over time, though it is still prevalent. Many parents of students with disabilities talk about how much their children resist getting accommodations due to not wanting to seem different, rather than having students reaching out to grab any and all special treatment.
Also, colleges and universities are not required to allow accommodations requested if the accommodations would fundamentally change the parameters of the course/how the course works. IEPs and 504 plans are only operational until the end of high school. Many colleges require updated testing to consider giving accommodations, and accommodations are much more limited at the college/university level.
Each professor also figures out what accommodations work for their classroom. For my student with disabilities, the disability office contact their professors at the start of each semester with the fact that they have accommodations and let the professors know what accommodations the student has. The professors then decide which ones work within for their specific course.
I find there are lots of anecdotes of over diagnosed disabilities allowing unfair advantage, but very little actual data supporting that.