The last time they had plenty of stock and cards people wanted to buy at the same time was the RX 200 series. They sold lots of cards, but part of the reason people wanted them was because they were priced fairly low because the cards were sold with low margins, so they didn’t make a huge amount of money, helping to subsidise their CPU division when it was making a loss, but not more.
Shortly after this generation launched Litecoin ASIC mining hardware became available, so suddenly the used market was flooded with these current-generation cards, making it make little sense to buy a new one for RRP, so towards the end of the generation, the cards were sold new at a loss just to make space. That meant they needed to release the next generation cards to convince people to buy them, but as they were just a refresh generation (basically the same GPUs but clocked higher and with lower model numbers with only the top-end Fury card being new silicon) it was hard to sell 300-series cards when they cost more than equivalent 200-series ones.
That meant they had less money to develop Polaris and Vegas than they wanted, so they ended up delayed. Polaris sold okay, but was only available as low-margin low-end cards, so didn’t make a huge amount of money. Vega ended up delayed by so long that Nvidia got an entire extra generation out, so AMD’s GTX 980 competitor ended up being an ineffective GTX 1070 competitor, and had to be sold for much less than planned, so again, didn’t make much money.
That problem compounded for years until Nvidia ran into their own problems recently.
It’s not unreasonable to claim that AMD graphics cards being in stock at the wrong time caused them a decade of problems.
Thermal problems are much less likely to kill hardware than they used to be. CPU manufacturers have got much better at avoiding microfractures caused by thermal stress (e.g. by making sure that everything in the CPU expands at the same rate when heated) and failures from electromigration (where the atoms in the CPU move because of applied voltage and stop being parts of transistors and traces, which happens faster at higher temperatures). Ten or twenty years ago, it was really bad for chips to swing between low and high temperatures a lot due to thermal stress, and bad for them to stay at above 90°C for a long time due to electromigration, but now heat makes so little difference that modern CPUs dynamically adjust their frequency to stay between 99.0° and 99.9° under load by default. The main benefit of extra cooling these days is that you can stay at a higher frequency for longer without exceeding the temperature limit, so get better average performance, but unless your cooling solution is seriously overspecced, the CPU will be above 99.0° under load a lot of the time either way and the motherboard just won’t ramp the fan up to maximum.