This code is so valuable I doubt anyone will just opensource it. And it's far from easy to write, as someone said there is probably only a handful working ones out there.
The same could be said about bruteforce code. Many years there was only crappy and slow LBC, then I payed a rather modest $450 to freelancer to fund opensource vanitygen fork.
In the same time Bitcrack was already done and also opensource, just not popular.
In result, as I can see, author of Bitcrack was donated several times with 0.1 BTC. That's better than nothing (a doubt he could use same resources as zielar)
There are few people involved in the puzzle that have resources, knowledge in programming and also "cracked" more or less puzzle addresses, so they have also money but they don`t want to share the tools like Pollard kangaroo script or other.
Like our world works, the power is in the hands of the few.
Later EDIT: Some guy asked me 0.30BTC for Pollard gpu script. Is more expensive than my car so I'll say pas