I’ve been using Ardour for many years, not only as a user but also a packager. I consider myself a huge fan of Ardour: I paid for it when I could afford it, I actually read and modified some of its source code (and dabbled with the Lua API), I contributed to the bug tracker, I regularly read this forum and even follow your work (repositories) and Paul’s (such as his posts on sites like HN and interviews) on the web.
And despite this, I did not know about the existence of bug bounties! Turns out it’s a field (Sponsorship) on MantisBT. So maybe the idea is right, but the system (bolted-on to tickets on the issue tracker, with no certainty that the money will actually be sent!) is IMHO not suited for attracting professionally-minded contributors, because there are issues of visibility, usability and trust.
A disclaimer: I hugely appreciate that some kind users offered their money. That’s more than most users (including myself) do, really, and if everyone pledged $3 to a ticket of their liking, the cumulative amounts would be decent. So please, don’t interpret my next paragraph as against what some kind and fair people decided to offer, but rather as evidence that the current system is not working.
Once what I said above is clear, I have to say that those rates are not acceptable for any programmer and I can’t blame anyone for not taking them. One thing is volunteering your time for free (which I myself gladly did for some smaller projects), another is accepting as little as $25 for a feature which likely requires at least some hours of study of the Ardour codebase before being able to write any code. I am not saying a FLOSS project should pay market rates for programmer’s time, just that IMHO a proper bug system has to offer amounts of money which are at the very least encouraging. IMHO, the only people willing to work for that sum can either earn more on Fiverr or Upwork or work on it for free because they are hobbyists with another day job or retired.
A more structured way bounty program is also likely to attract companies and musicians who work with Ardour and not just hackers who can operate an issue tracker.
In short, volunteering is hugely noble and important but so is paid work when it contributes to the common good (GPL’d software, in this case). Some things (such as contributing to Ardour) require advanced skills, which are are highly remunerated in the job market. In order to attract professional contributors, bounties need to be at the very least proportional to the hours of work needed and parametrized (at the very least) to a programmer’s average salary in a developing country, other than trusted (so, it’s OK if a trusted entity actually collects the bounty money as soon as it posted, paying it after the commits are merged).
Besides, harrisonconsoles.com does hire contractors to work on Ardour. The problem is that there is “so much to do, and so little time” 
Did not know about it, I apologize for having jumped to wrong conclusions! But it’d be nice (for Harrison too, it’s good PR!) if users knew more about Harrison’s contributions to Ardour.