How was the Candidate chosen for 1927, and why not sooner? Wikipedia has a tiny article for the 1927 World Chess Championship. For the World Chess Championship article in general, it has very little to say about the 1927 one:

Following the controversies surrounding his 1921 match against Lasker, in 1922 world champion Capablanca proposed the &quot;London Rules&quot;: the first player to win six games would win the match; playing sessions would be limited to 5 hours; the time limit would be 40 moves in 2½ hours; the champion must defend his title within one year of receiving a challenge from a recognized master; the champion would decide the date of the match; the champion was not obliged to accept a challenge for a purse of less than US$10,000 (about $140,000 in current terms); 20% of the purse was to be paid to the title holder, and the remainder being divided, 60% going to the winner of the match, and 40% to the loser; the highest purse bid must be accepted. Alekhine, Bogoljubov, Maróczy, Réti, Rubinstein, Tartakower and Vidmar promptly signed them.


The only match played under those rules was Capablanca vs Alekhine in 1927, although there has been speculation that the actual contract might have included a &quot;two-game lead&quot; clause. Alekhine, Rubinstein and Nimzowitsch had all challenged Capablanca in the early 1920s but only Alekhine could raise the US$10,000 Capablanca demanded and only in 1927.

I bolded the main relevant points, but I still don't understand how the 1927 WCC worked.
First of all, it lists Alekhine, Bogoljubov, Maróczy, Réti, Rubinstein, Tartakower and Vidmar, but it doesn't say how the candidates tourney was organized or how it went. How was the candidate chosen? And when? Was it some round robin format?
Second of all, I still don't understand why this was delayed until 1927. Capablanca became champ in 1921. It says only Alekhine could raise the money but that leaves out some information, to say the least. Weren't the other candidates involved somehow for the candidates tourney and surely must have been able to raise something?
I realize ofc this is the Pre-FIDE era, but surely there are better records than this for the WCC?
I did find a little more info on a chessentials article.

During the London Tournament, Capablanca and Rubinstein agreed their potential match would take place only in 1923. However, it was precisely due to the „Golden Wall“ rule that their match never took place; Rubinstein was simply unable to collect this enormous sum of money.


Neither were Capablanca’s next challengers – Marshall in 1923 and Nimzowitsch in 1926 able to do so. Alekhine was also unable to find financial backers until 1926 when Argentine Chess Federation offered to sponsor the match. Capablanca agreed to the match, but only if Nimzowitsch, whose challenge was pending at a time, would be unable to raise the funds until January 1, 1927. Nimzowitsch was unable to do so, and Alekhine – Capablanca 1927 match was finally agreed.

So apparently Rubenstein was the first candidate, then Marshall, then Nimzowitsch. However, it's still not explaining how those were chosen, or how the Candidates Tourney was played out.
...Was there no Candidates Tourney at all back then?
How was the candidate chosen?

Very simple. Money. The first to raise the $10,000 stake.

And when?

As soon as possible.

Was it some round robin format?

No. First to put $10,000 on the table gets to play the match.

Was there no Candidates Tourney at all back then?

Correct
This is explicitly stated in the Wikipedia article you reference:

From 1886 to 1946, the champion set the terms, requiring any challenger to raise a sizable stake and defeat the champion in a match in order to become the new world champion