I can't speak for the whole market, but in the sectors I casually follow (electric vehicles, tech, airlines), there were legitimate reasons for the rally:

ELECTRIC VEHICLES: A LOT of new electric cars have finally entered their production runs this year. It just so happened that 2020 was the year in which many manufacturers planned to drop their answers to the Model S/Model 3. Remember: big auto usually plans in 2-3 year increments, so all of the options you're seeing now were potentially drafted up back in 2017-2018 when the Model 3 entered production.

(The Model 3 was really what lit a fire under everyone's ass. Big auto saw that Tesla could produce a car that is mainstream-affordable without compromising on mileage, battery tech, or safety. That + Tesla making most of the car's core features built into software (which kills the whola idea of options and packages, a HUGE moneymaker) and their world-class driver assistance tech meant that automakers had to do _something_. People love to hate on Tesla, but the Model 3 is really what started Tesla's share price rocketing to the moon.)

There have also been significant advancements in the fast-charging networks available for these cars. Electrify America has grown a lot in 2020, likely due to COVID and businesses preparing for re-opening in 2021. Tesla has significantly expanded their network as well. The theory is that businesses that add fast-charging stations to their parking lots (and actually _enforce_ them) instantly gain access to a small, but growing, set of affluent consumers with time to kill. No better time to build these chargers than when everything is closed, assuming that you had the spare cash to do it. (Tesla pays for everything if they select your site as a supercharging location; it's an awesome incentive to bolster the network.)

AIRLINES: A rally was pretty much inevitable. COVID absolutely killed demand for travel, but "everyone" agreed that flying was going to happen again once we got the virus under control and a vaccine was made available. Additionally, COVID fast-tracked several aircraft retirements that were going to happen years down the line. American retired the B767 last year, Delta the MD80/MD90, Emirates the A380. COVID also forced airlines to rethink their digital strategies (to respond to fast-changing CDC standards) and think outside the box for other revenue streams (American's wine subscription comes to mind). All of these things made airlines more efficient, which is usually rewarded through their EPS.

Additionally, Boeing was finally able to get the 737MAX recertified by the FAA after. The 737MAX brings great fuel efficiencies and longer range over the 737NG models. Pretty much every airline is going to add several of these to their fleet. There's also the 777 replacement that's on the way that promises similar fuel efficiency gains and potentially longer range. (I'm hoping that it can do DFW-DEL, but I'm not holding my breath on that one.)

TECH: First of all, holy shit, like, A BILLION companies IPOed in 2020. It was like COVID didn't happen. Also, think of how many companies saw absolutely maniacal growth due to the world instantly going remote: food/grocery delivery (Instacart and DoorDash especially, doubly so in regions were delivery wasn't normally popular), any company that did videoconferencing (remember last March when basically EVERY cloud provider was short on hardware because of the sudden demand for VC?), EdTech, etc. The only tech companies that were directly affected by COVID were ones that were in the industries that were directly affected by COVID (travel, hospitality); to everyone else, it was basically turbulence.

In fact, I remember companies were going on hiring sprees during the first and second wave. Anecdotally, my inbox was ON FIRE during this period. This made me feel bad: in a world in which millions were losing their jobs, I had more choice than ever before...

GENERAL NOTES: The other thing to consider is that special-purpose acquisition companies (SPACs) and direct listing became really popular in 2020. This made it possible for companies to get access to capital much more quickly. So many companies are going public through SPACs: WeWork, SoFi, Lucid, hell, even fucking TOPPS (yes, the baseball card company) is in this game now. It's great for retail investors (they can get in at pre-IPO prices without having to be accredited investors or a having private bank account with lower risk than going through secondary markets), great for businesses (since they can go public more quickly), and great for the SPACs (since they take shares off the top and make insane money once the merger completes)