I don't see what is so difficult to understand here.
That might be because you have the mental fortitude of a 5 year old. I'll humour you, though, and will take it slow.
1. Udinese is not and never will be a top club.
Why? Because it's a city of like 170K in Northern Italy surrounded by massive teams from large cities. End of.
So what does that mean?
a.) They will never be able to hold onto top/very good players if very large teams come at them. Plain and simple. So posting some fantasy lineup means absolutely nothing. Barca, Inter, Juve, Lazio and Napoli are all bigger clubs that can offer those players more glory and more money. Selling players is nothing new.
b.) They have to come up with a model that gets the most out of their means and potential - not just right now but in 10 years time. Yes, that's a novel concept in Italy, I grant you. A new stadium, in part financed by sales mentioned in a.), will be the foundation for that model.
2. Success is relative. For a club like Juve, success means winning the scudetto and competing in the CL. For a club like Udinese it means staying between mid table and european spots. They are doing that consistently these days and increased revenue from 3. will make competing for European spots the norm.
3. Owning your own full service modern stadium is a pretty fucking big deal in Italy. Not only when it comes to status but mostly finances. If they pull this off they will start milking the maximum out of their tiny catchment area. We build restaurants and hotels around our stadium too - welcome to the future.
I hope this clears it up for for you.