If it is challenging to please an entire player base with the new HUD, whose idea was it to keep it from being fully customisable? This is not only appreciated by the players, but heavily requested from the beginning (as a feedback).

My experience in game design is that players always ask for the most customization possible. All things being equal, the assumption is nearly always that 100% customizable is always better than no customization. There are a number of reasons why we don't believe that to be the case: competitive integrity, the potential to cause glitches or get things in an unplayable state, the resource needs it takes to support and develop all of those options, and so on, but most importantly: it is weasely game design to say "We developers really don't know what a good experience is, so we're just going to give you a big tool set and hope you can find something fun." The trick is to offer those options or customizations that are important. An example I use frequently is inverting the Y axis for camera controls on a mouse or controller. It is an expected option these days, and you're not going to win the battle with players by trying to claim that one design is better than another. If you follow the guideline of offering the most important options, and we might very well add others to the HUD over time, then you end up with an options page or two rather than 40 pages of options to scroll through that many players won't be able to decipher. We think a smaller number of important options is more important than a virtually limitless number of options.