fights that should have happened?

Why do fighters make excused to duck other top fighters instead of giving the world what they want.

Mayweather vs Pac
Obvious fight that should have happened years ago. It's always reported that Mayweather has some kind of excuse not to fight Manny. He has ducked Pac for a long time now.

 

Lamotta vs Graziano

It's hard to see how this fight never ended up happening. Jake LaMotta and Rocky Graziano were two of the top middleweights, both briefly world champions, during the division's true golden age.
The two Italian-Americans shared similar backgrounds, having grown up in the New York City ghettos. LaMotta was a native of the Bronx, and Graziano represented Manhattan's Lower East Side. One story I've often read or heard repeated among boxing fans was that the two never fought, due to their friendship.

Rocky Marciano vs Floyd Patterson
Rocky Marciano is one of boxing's enduring icons, the only heavyweight champion to retire with a perfect record. But among boxing historians, the quality of his opposition receives legitimate criticism.
His three biggest wins came against Ezzard Charles, Joe Walcott and Archie Moore. These are three all-time greats, but they were all on the backside of their primes when they faced Marciano. Walcott and Moore were both ancient, by prizefighting standards.
If Marciano had not chosen to retire and vacate the title in April 1956, Floyd Patterson was the obvious No. 1 contender for his belt. Instead, Patterson became the youngest heavyweight champion in history, when he captured the vacated belt by decisioning Archie Moore the following November.

 

Hearns vs McCallum

In the mid-1980s, Mike McCallum was the undefeated, WBA junior middleweight champion. The beginning of his reign coincided with Thomas Hearns' own term as the WBC champion at 154.
Of all the fights I've listed here, this one might have had the greatest potential for achieving legendary status. Hearns was possibly at his very best fighting at 154, but he never faced anybody there who was as potentially dangerous to him as McCallum was.

 

Mayweather vs Paul Williams

After Mayweather beat Hatton he temporarily left boxing for WWE. This reason could have been because would have had to face Williams. He has notable victories over world champions such as Winky Wright, Kermit Cintron, Carlos Quintana, Sharmba Mitchell, Erislandy Lara, Sergio Martínez and Antonio Margarito who he took the Welterweight title from in 2007. A motorcycle accident on May 27, 2012, paralyzed him from the waist down, ending his boxing career.

 

How Mayweather has got away with ducking dangerous people in their prime is well out of order. Even making fighters fight at a catch weight like he did Canelo. He does anything he can to get the upper hand.

Would have lived to see him fight a prime Margarito