In earlier times, measuring equipment wasn't accurate enough, so races had to be done in parallel with people starting at the same time. Today, that's no longer necessary. In fact, people racing one after another is exactly how we hand out world records.
Of course, the Olympics and other events like them aren't there to find the best athletes in some absolute sense; these events are there to entertain spectators. Otherwise, swimmers could just do time trials at home and mail in times.
And spectators like people racing each other at the same time.
Additionally, it would make races take 8x to 10x amount of time.
Yes, it's more fun.
> Additionally, it would make races take 8x to 10x amount of time.
Well, that's not a problem, they can run different events in parallel. Eg swimming and running shouldn't interfere at all with each other.
They already run events in parallel.
While that's technically true, the drafting effect actually means that being a bit more than a body length behind the swimmer next to you is beneficial to you. That's another part of the philosophy why the fastest swimmers are assigned the center lanes, and the slowest the outermost lanes, to balance out the choppiness of being by the sides with creating a potential for drafting. Of course intentionally drafting is not a strategy that will win you the race, especially in short events, but in longer events it can be important to keep pace with the swimmer next to you while they need to expend more energy and you draft off of them either with the intention to eventually pass them or to stay ahead of the swimmers on your outside.
In cases where there are less swimmers than lanes, they leave the edge lanes empty.
Putting the faster qualifiers in the middle lanes is also a better view for the spectators on both sides of the pool.
Olympic and similar competitions are timed to the nearest 1,000th of a second, but any result within the same 100th is considered a tie as that last bit is just entirely arbitrary, in part because pool dimensions themselves are not accurate to this degree. (The FINA standards mentioned in my earlier comment addresses dimensions accuracy standards.) The Olympics did break ties at the 1/1,000s standard in 1972, but has since judged any result within 1/100th as a tie:
<https://olympstats.com/2014/02/12/timing-accuracy-at-the-oly...>