In this solution, we will identify the reason why leaders have difficulty in implementing their visions and strategies.

$2$

Let's analyze the options provided to determine the most appropriate one.

a$.$ It's worth noting that teams, systems, and organizational processes are important factors that impact the effectiveness of implementation.

However, the problem presented here pertains specifically to the challenges in implementing vision and strategies, not to the process of implementation itself.

Therefore, this option is incorrect.

$3$

b$.$ If the budgeting and control systems are not properly in place, they can restrict the resource allocation, along with effective tracking of the progress.

Also, when there is a misalignment in budgets, followed by rigid control systems, leaders often find it tough to align the organization's tasks and activities to the vision and strategies.

Therefore, this option is correct.

$4$

c$.$ When an organization does not have enough mechanisms in place to ensure coordination and integration, it can cause hurdles in the overall implementation process.

This factor does not focus on vision and strategies, but the entire process.

Therefore, this option is incorrect.

$5$

d$.$ Though accountability is very important to improve organizational performance, it does not directly address inefficiency in the implementation of vision and strategies.

Therefore, this option is incorrect.

$6$

Based on the above discussion, we can conclude that the most suitable option is B$.$