Actually, while learning the English alphabet is much easier than learning characters in East Asian languages, most linguists I’ve talked with and read have cited English as one of the hardest languages to learn from a grammatical and pronunciation/phonics standpoint.
There’s far too many exceptions to general rules which trip up not only immigrants and foreign learners, but also native-born folks in nations where English is the/one of the official languages. A large part of that is due to the English language haphazardly adopting elements from Germanic and Romantic French/Latin languages from the European medieval period onwards.
As for the prevalence of English as a second language across the world, a large part of that is due to historical factors such as the rise of the British Empire from the 18th century and the rise of the US as an international commercial and political/military power in the late 19th and early-mid 20th centuries. Not because English is necessarily easier for most people to learn.
If the Spanish, Dutch, or the French had defeated the British in critical battles during the 16th-18th centuries, it’s likely the prevalent second language internationally would have been one of those rather than English.
Come to think of it, if Zheng He’s overseas voyage in the early Ming era hadn’t stopped in East Africa, but had continued into late medieval/early renaissance Europe with their political disunities/wars, the second language internationally may have ended up being some variant of Chinese rather than English.