For privacy reasons the official list of merit sources is not publicly available, we wouldn't want users bugging the sources for merits or scrutinizing their merit awarding.
There is NOTHING PRIVATE about this. Absolutely. Such a list of active sources can be made easily and simply. Just go to BPIP, go to the SENT rating tab and see the users who distributed more merit than they earned. This is sources. I myself can make such a table in a day and there will be nothing extra secret in it.
The only thing is that it will not always be possible to accurately determine whether this is an active merit source or no longer.
If you need effort to know who are the merit sources, many people are less likely to do it which leads to less people bothering merit sources.
I feel handing out 50 merits in one lump is lazy and shouldn't be allowed to occur.
In many cases i would agree, but there are few cases where amazing post/thread deserve 50 merit.