First, let's start with MTTF. It means Mean Time To Failure, so here's your first clue. Basically this whole formula should tell you how long it takes to reach failure, therefore, time affects every single thing here.
Then, let's dig deeper. Notice how you first have material properties and geometry (A) divided by current density. More current density in same silicon will shorten it's lifespan, but besides that, the worst thing is that exp part, meaning exponent, which means material properties of silicon and current density will lead to failure by factor of exponent. Now Q is activation energy, in semiconductors meaning voltage (not threshold voltage, but maximum power state voltage, meaning voltage required for achieving high clock speed). And then you divide it by Boltzman's constant multiplied by temperature in Kelvins (which barely variates as 0C is around 270K, idling GPU is at around 310-320K and at full load it may be at 340K-380K), meaning that voltage itself and alone will affect lifespan of semiconductor much more than temperature ever will and in some amount of time. I won't calculate it, because I'm really awful at physics myself, but it's pretty obvious too, undervolted card will only get like 10-20% voltage reduction and perhaps loss of 10 kelvins, which is like 2% reduction. So even considering the fact that it's an exponent, you may double the lifespan of your HW, but if you keep it on for 6 times longer, then it just means have to have a seriously aggressive undervolt and underclock to make your card's wear and tear similar to gamer's, which is not going to happen, because performance is crucial and you just end up with card that are at best (meaning that user cared to undervolt and keep them well cooled) are like 2 years old, but already are as worn out as 6 year old cards and that gets seriously worse very quickly. If person never undervolted them and kept them cool, card that is 2 years old will already have been worn out like 12 year old card. That's a big problem, because absolute minimum MTTF for desktop hardware is 5 years. Now, that MTTF number is probably calculated in 24/7 type of usage, because predicting average usage is way too subjective, but still, my point that you may buy way too worn out hardware for its age stands.