What did Donquixote family lack to obtain a status of an Emperor?
When Garp talks about the Yonko he describes the way how they rule the 2nd half of the Grand Line, like Emperors.
From what we have seen, what makes an Emperor are first and foremost, a large crew.
Secondly, territories that they rule over or use their name to protect them.
Thirdly, the influence in the seas where they operate.
Let's start with influence. It's certainly an area where Donquixote didnt fall short. Doffy was one of the most influential characters in New World and his operations reached out to Paradise as well. He was seen in Jaya where his underling Bellamy operated and his operations were noted in Sabaody. Ultimately, as Joker, he was the man who ran the Underworld in New World, many countries were depending on his operation. The whole SMILE operation was possible because of him. His influence even reached to the top of the World Government, he blackmailed them into fooling the entire world just for his scheme of fooling Law and SHs.
When it comes to territories, he certainly doesnt lack in that section either, with the whole Dressrosa under his command he fulfills that requirement.
Human auction in Sabaody was also his territory, ran by his influence and connections until he abandoned it. Considering that other Emperors dont have more territories necessarily than their headquarters, this certainly isnt a reason why Doffy isnt an Emperor, especially considering that Luffy was proclaimed as Emperor without a single territory that could be called his HQ. With Vergo and Monet monitoring and protecting Caesar, Punk Hazzard could also be considered his territory.
When it comes to having a large crew, Doffy should check this one as well. His troops counted over 2.000 men, that may be short compared to the number the Emperors command but compared to Shanks or Blackbeard, depending on how many they command, may not be short after all. When it comes to notable members, Doflamingo family probably counts more than RedHair and Blackbeard Pirates who have around 10 notable members. Doflamingo had 4 commanders under him, called Seats. All Seats commanded 3-4 notable members under them, aside from Vergo who was on an undercover operation. There is also Monet whose hierarchy is uncertain.
The most terrifying powers in his organization, especially in Dressrosa setting, were the abilities of 3 characters - Doflamingo's Birdcage which prevents the enemies from escaping as well as cutting off all communications and prevents help from coming in. In such limited space which constantly shrinks, we have the country-wide terraforming ability of the Seat, Pica. While ridiculed by downplayers, we now see that his powers are of more use than all Calamities and Sweet Commanders put together. On top of those two abilities, we have the ultimate trump card, Sugar, with the frightening ability which neutralized many threats in Doflamingo's way.
So, considering that Doflamingo checks off all the requirements that make an Emperor, why wasnt he one of them?
The first objection could be that he himself wasnt individually strong enough. Luffy became an Emperor when he demonstrated proof of strength and his commanding troops became known. Doffy is a strong individual, not on the level of other Emperors but still, he wouldnt be a Warlord if he wasnt incredibly strong himself(Buggy-senchou aside). The number of troops required to defeat the Doflamingo family was comparable to a number of troops currently fighting an Alliance between two Emperors, granted that aside from Big Mom herself and Perorin, nobody else from BMP are there as of now.
What is your opinion regarding why Doffy fell short of Emperor status?