For example, Hunter and Queens College are not very competive schools. But their acceptance rates are both below 30%. So do other CUNY college, what make them so selective?
Many under qualified people apply.
ya too many stoopid peple
Because CUNYs are so cheap and so many people apply to them. So, of course they’re only going to pick the best of the best.
CUNY was once an outstanding system. A lot of well known scholars got their degrees there in previous generations. Then CUNY went to open admissions in 1970 and it was a disaster. CUNY became a joke-a remedial school for people who could barely earn the GED. But in 1999 open admissions ended and, at the same time, CUNY began to advocate to improve the system in general and protest disparities between conditions at CUNY and SUNY. That ushered in considerable growth and improvement. Now CUNY has some of the most competitive and rigorous programs in the NY system.
Applicants may not always realize how competitive some of the programs are.
CUNY are so cheap, thousands of people - internationally and nationally fight for one seat. Competitions are naturally going to be rougher than other private colleges.
CUNY is a fantastic system especially for individuals who are planning on going to graduate school, whether it is law or medical school etc. You leave owing close to nothing and you don’t even need financial aid, because a year is like 6 grand for in-state tuition. So if you have a job, you can pay for school with payment plans. As for quality education; my sister attends Hunter college and I go to CCNY. Her neuroscience, research partners from NYU look at her Orgo work and were confused at how difficult it is. lol. Just because it’s affordable doesn’t make CUNY easy. If you apply to the CUNY senior colleges, particularly Hunter, Queens, CCNY, Baruch, Brooklyn and even John Jay, don’t expect an easy ride. CUNY expects a lot from their students. 
Many under qualified people apply.
That is true of even the most selective Colleges in the US. The CUNY schools have been the defacto destination for NYC students, whose parents are immigrants and cannot afford Colleges with much higher tuitions. For a lot of CUNY students, even $6,000 a year tuition (New York State Resident) is considered high.
Grove School of Engineering at CCNY, attracts a large number of very smart Engineering students from outside of the US, many of whom have to pay “Out-of-state/International” tuition, which runs about $560 per credit ($17K per year for 30 credits). A significant number of CUNY students are independent students, who typically have to work full-time/part-time to support themselves. The fact that it is no longer an open enrollment system, it has become very selective and have attracted higher caliber students via their Macaulay Honors College/Honors program. Some of their Professional Programs (ADN/BSN Nursing, Engineering, Physician assistants, etc.) are very popular due to the cost and quality of their programs.
What also isn’t being said is that you apply to CUNY and put your first second and third choice down and this is only one application fee. So people will put down the higher end schools as more of a “well if I can get in, great, but I know I am not up to the level.” Even if you put ONE school and don’t get into it, they will look at your major and offer admission to another CUNY with that program.