Just to flatter them so that they got land to stay on and could get an easy access to the trade with the people of that country. They would also get special provisions such as no duty charge, while they imported or exported goods to their homeland from the trading country and vice versa.
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Just as their offerings in the hope that they will get the benefits in the form of reduction in revenue , tax etc... 

Because they what to be grateful or they just want back a gift from the king like a job, no more tax and free food