”A lot of talent sitting in suits” means a lot of talented players are not playing.
Former commissioner of the NBA, David Stern, ratified the NBA dress code in 2005, which requires all players not playing that game to wear formal attire. So if a player shows up wearing a suit, he's probably not playing that night.
Wikipedia - NBA dress code:
Stern's dress code stated that all players must dress in business or conservative attire while arriving and departing during a scheduled game, on the bench while injured, and when conducting official NBA business (press interviews, charity events, etc.).
The original NBA Player Dress Code:
General Policy: Business Casual
Players are required to wear Business Casual attire whenever they are engaged in team or league business.
"Business Casual" attire means
A long or short-sleeved dress shirt (collared or turtleneck), and/or a sweater.
Dress slacks, khaki pants, or dress jeans.
Appropriate shoes and socks, including dress shoes, dress boots, or other presentable shoes, but not including sneakers, sandals, flip-flops, or work boots.
According to Wikipedia, NBA is the first major professional sports league to implement such a rule. I'm not sure if there are other professional sports leagues that have similar rules.
By the way, to leave some context of what Lebron's talking about for future reference, today's NBA Injuries:
Cleveland Cavaliers: (Name / Status / Date)
Anderson Varejao / Out / Jun 17
Comment: Varejao (Achilles) was limited to 26 games after signing a contract extension. He averaged 9.6 points and 6.5 rebounds before going down for the season in late December.
Shawn Marion / Day-To-Day / Jun 17
Comment: Marion did not play in the NBA Finals. He did not top six minutes in the Cavaliers' playoff run. The 37 year old averaged career lows 4.8 points and 3.5 rebounds in 19.3 minutes.
Kevin Love / Out / Jun 17
Comment: Love (shoulder) averaged 16.4 points and 9.7 rebounds in his first year as a Cavalier. His season ended in the first round of the playoffs as he tussled for a loose ball with the Celtics' Kelly Olynyk.
Kyrie Irving / Out / Jun 17
Comment: Irving (knee) averaged 21.7 points and 5.2 assists in a career-high 75 games in 2014-15. He was hobbled by injuries in the playoffs and finished the season with a fractured kneecap in the first game of the Finals.