It is a good question, and as far as I've looked into it, I think it's mostly down to "cosmetics". They think it looks cooler, more modern.

There could be a benefit to cooling of brakes, since the extra space will allow for better ventilation, but it will also require a large revamp of the suspension. Similarly, it could, in theory, allow for bigger brake discs. The extra ventilation could however also affect aero negatively of the cars due to uncontrolled air movements.

If I recall correctly, the change is however negative in terms of traction in the corners. The change also demand a pretty big revamp in how they design their suspensions. I believe they are moving towards active suspensions again, mind, so a big revamp was coming anyway.

I was afraid of the cosmetics argument, when they're lamenting the fact of weight increase. But then I started thinking about cost reduction, thing like suspension geometrics changing due to larger wheels, and also brakes being bigger and perhaps then allowing for cheaper materials. I don't know, this is so above my level it's not even funny. Anyway, my first thought was when they all said: "We're sorry but the weight will increase, and its due to the wheels to a large degree.", well then why change it? Like Hamilton said, a weight increase increases the stress on the tires, and if the dimensions of the wheels also does that, it's like a double negative.... I sure as shit don't get it..... This is the one thing about the new rules I dont like, (and it should have been 150 mil not 175 mil in a cost cap)

I'm all for cosmetics, but it shouldn't come at the expense of performance. I get they wanted to make them look cooler, more road car-like, but I also think it's a silly reason to compromise the racing. I don't think they could afford getting cheaper brakes due to this change, sadly, but it would be a nice bonus where it so. IMO, it stinks of "change just 'cuz", and that ain't good. It's one of the less positive sides since Liberty's takeover, one that I can bear but still find a bit silly.

As for the budget cap: I find it's kinda in the sweetspot. Considering it'll cut Ferrari's, Merc' and RBH's budget with nearly 1/3rd, that's a significant cut, but it'll also allow the bigger spenders to keep spend big, just not as silly big, while also emphasizing cost efficiency. It's such a change that could reintroduce interest from the likes of Toyota and so. I also feel that such a hefty cut will greatly benefit the likes of RP and TRH, cost efficient midfielders.