Mexican billionaire Carlos Slim was the biggest loser among the world's top 400 richest people this year.

According to Bloomberg Billionaires Index, Slim lost $20 billion in 2015, lowering his fortune to $52.8 billion, and dropping the executive from third to fifth-richest person alive.

Due to regulatory pressures in his native Mexico, Slim's America Movil SAB telecommunications company was forced to share its infrastructure with other mobile and fixed-line suppliers, setting it up for its largest loss since 2008.

Slim owns 57 percent of the Mexico City-based telecommunications giant, which used have a firm hold on having most-weighted stock on Mexico's benchmark index. That position was recently taken by bottler and convenience store operator Fomento Economico Mexicano SAB (Femsa), after America Movil's stock dropped by 18 percent.

In addition to the new regulatory practices, America Movil is facing a number of obstacles, including stronger competitors in Mexico, a worsening economy in Brazil (its second biggest market), and limited options for expansion in Europe.

"There really isn't anything near-team to get investors excited so the focus has turned to the deteriorating profitability in the Mexican market," said Kevin Smithen, an analyst with Macquarie Securities USA Inc., in an interview with Bloomberg.

In order to boost stock prices, Smithen said, "You really need to see a more credible expansion strategy in Europe or evidence of a financial turnaround in Brazil."

America Movil controls 70 percent of mobile phones and 62 percent of fixed lines in Mexico, numbers that are quickly dwindling. AT&T Inc. has also encroached on the company's territory, with its purchase of rival businesses, NII Holdings Inc.'s Nextel Mexico and Grupo Iusacell SA.

"The change in telecom regulations in Mexico attracted competition, and now AT&T is investing heavily to create a strong mobile player in the country," Credit Suisse analyst Daniel Federle said in a report via Bloomberg. "Competition will get tougher in the following years."