I think Beterbiev benefitted from being under estimated. He never had the boogeyman label (like GGG did despite being the superior fighter) so others weren't afraid to fight him. Everybody thought he was this big dumb oaf without any skill and would be found out. Turns out there was a lot more skill to him than almost anybody had credited him for.
Is there any evidence that an official offer was sent to any of the names you mentioned and they decided not to accept it? Virgil Ortiz's camp mentioned that they were in talks to try and make a fight with Ennis, Fundora, even mentioned wanting to reach out to Spence..... Haven't heard much coming from the Kelly and Lubin camp...... All these chants about "this man is being ducked" and "that man is being ducked" has gotten old..... It seems everyone who doesn't get the fights their heart desires claim they are being ducked and/or their fans start a movement to suggest he is being ducked........ And very rarely do with see any evidence that showcases that the protocol needed to make the fight happen was done. It's always......"send the contract" or "he called him out in that interview"........as if it's all that simple. GGG was different. There were individuals who actually left the divisions and/or turned down official offers to face him.
Short term payday vs long term payday. If he wins the belt, he can command the lion's share of the purse against any opponent, including Ortiz. If he think he's going to lose against Murtazaliev, then it's better to take bigger payday against Ortiz, another fight he'll probably lose.
What happened to the folks who keep saying fighters are never scared? Of course they are. They might not be trembling but ducking is fundamentally based on fear of losing. Fighters know what's up when they see a savage in the ring.