The first main reason is that the onboarding dates entirely depend on no of projects, vacancies,laying off high billed resources etc in these companies.
The next maybe the onboarding is going on but it is going maybe for your previous batches,im not sure too.
I too saw many people from recent batches commenting and posting they didn't receive joining date for a year.
I was onboarded during covid time, as you know that time long lockdown and many layoff happened too. To replace these layoff resources new joiners were onboarded ASAP. U might have heard about the Market in 2020-2022.