Good day, Aga,
More and more people are deciding to travel abroad. - In this scenario, people are likely to shift towards traveling abroad as time passes. The continuity of time links the meaning to a gradual shift in the decision of some people to travel. (Present Continuous)
More and more people decide to travel abroad. - In this scenario, you have represented a regularity of the committed action in a way that might be attached to a specific time period, as if the seasons or months. (Present Simple)
Thank you for your question.
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If you have more questions, I will be more than happy to answer them on a private one to one lessons that I hold as a teacher on Italki.
Sincerely,
H.Kirishchyan