1. His contract holds the Suns back
The only reason the Suns were able to trade for Beal was because he made similar money to Paul, and he waived his no-trade clause. The logic in adding him when Durant and Booker are also on massive deals made sense from that standpoint, but it seriously restricts the moves the organization can make in future.
Starting next season, he'll be making over $150 million from then until his current deal expires. Booker's deal is similar although goes one year longer and reaches $62 million in a single season - not that anybody is complaining about that - while Durant's is up the year before Beal's but the numbers are again similar.
So as long as Beal is along for the ride, the front office are hamstrung (no pun intended...) in the depth they can surround their stars with. They've done an amazing job this season of getting Allen, Nurkic and Eric Gordon, while the Bol Bol experience feels like found money. But there are only so many times they can turn water into wine with this group.
The new CBA means that Beal could be traded for a player of equal salary down the road - as opposed to a collection of contracts - so that is at least some form of get out clause if required. But when you see who else is making that kind of money, it is equally as scary to lock yourself into those players. The reality is the Suns lost flexibility in trading for Beal, and they will likely come to regret it.