Dear Rupendra,
You wanted to provide access to the bank's website to which the salary credited but then you have not mentioned, which exactly is the bank. Anyway, you may quote the following reasons:
a) All the employees do not have computer or laptops in their home. Access to the bank's website will help them doing financial transaction(s) with ease.
b) While most of the banks have their own Apps, all employees may not be that conversant with these Apps. Secondly, these apps blocks Random Access Memory (RAM) of the mobile. Every employee does not have high-RAM mobile phones.
c) Reading general information about new rules or regulations is easier on the laptop or computer.
d) Banks' websites are not like websites of social media. Risk of spending time in unwanted activities is minimal. Employees will close the website once their job is over.
Thanks,
Dinesh Divekar