Pace of upgrades is a separate question from temper bricking, though.
Let’s say you brick an item 60% of the time (theoretically it’s more 30-40% with two 4-affix books on a 1-2 GA, but let’s say there’s some bugs that cause u intended weighting). That means that for every 2 upgrades you find, you are on average getting 5 drops that seem good enough to be worth tempering.
They could increase the pace of upgrades by improving your chances to not brick an item, but they could also do it by just giving you more drops. Or making more drops have GAs. So temper bricking isn’t the reason you don’t get upgrades, that’s a separate design choice. If they made tempering never brick, they would likely also give you 60% fewer drops to compensate.
Personally, I’d rather have 5 interesting drops with only 2 of them turning into upgrades than getting only the 2 upgrades.
The problem with tempering is that the high end of success is a small boost compared to the default, while the low end is a huge loss of power compared to the default. They need to give ways to use the extra rerolls when you do hit your affixes to further enhance one or both of the affixes.