Backlog:

Every year there's a finite amount of green cards available, and a rule that says: a country can not claim more than 7% of all the green cards each year.

So every year the max number of Indians that can get green card is the same as the max number of Portuguese, but India has 100x the population of Portugal, so if in proportion to their population, as many Indians applies for green card as Portuguese, the Portuguese have a much higher chance of getting it approved this year

The Indians who didn't get it because of reaching that 7% are added to a backlog.

The following year, the same thing is repeated, but now in addition, you have all the people in the backlog, ... Repeat that many years, and now the backlog is more than a decade long: people who applied for the Green card a decade ago are still waiting.

Yep, I'm going for my Greencard through the EB program, and because I'm from New Zealand my priority date (which is where the queue starts), is "current" which means the day the paperwork gets approved, things can move forward. If I were Chinese or Indian the priority date is years ago - the current Indian priority date for the EB3 is 2009.

It's already more difficult, expensive and time consuming to get a Greencard vs. permanent residency in comparable Western nations. My Greencard will take 18+ months, $15k and a very flexible employer and I'm walking into the system with a lot of advantages. I feel for Indians and Chinese people in the system.

A maximum of 7% per year can convert over from any one country. Countries likes India, Mexico and Philippines (and China?) have higher proportion so there is a huge backlog. Most other countries are significantly better.