My first answer to this question, a very good question, is simply because of what the Bible actually is. Remember that the Bible is a library of ancient documents that comes from three different continents, was authored by over 40 different authors, and was written over a 1500 year period. These cultures that God intervened in were truly & radically different from what ours is today. To fully understand a text one needs to be able to appreciate the cultural context. It would be no good for 21st century Westerners to interpret the Bible through a 21st century lens. Also, each author had their own unique reasons for writing, whether that reason was to write biography (the gospels), history (Acts), poetry (Psalms), prophecy (Micah) etc. These are vast fields of genres that all require sound interpretation.
It’s also when we want to try and understand the Bible for all that is worth that we then require apologetics. In other words, people begin to analyse the Bible to try and to determine its meaning, the author’s intent, how one section correlates with another. Now, since the Bible is taken so seriously then often every little detail is cause for major concern in the eyes of scholars, readers, believers & unbelievers alike. This is especially true since critics will look for any excuse to discredit & undermine the Bible. Again, apologists ought to have answers for these critics.
Furthermore, since so many different people read the Bible it will inevitably be the case that some of them will be mistaken in their interpretation. Who is correct and who is wrong is up for debate, and here the apologist’s job is to show just where a person has gone wrong in his exegesis.
Then there are also many roadblocks one may have to faith. Christians might be troubled with certain verses for certain reasons and of course they will look for answers. If their questions are left unanswered and their doubts, as a result, grow they could very well leave the faith. Therefore, answering obstacles to belief is important. On the same note there are also misconceptions. Some people make it their goal to undermine the Bible wherever they can. And of course one is required to answer them especially since they can have a wide influence on many people through the use of memes, pictures, or videos on the internet. Other times there are just blatantly poor arguments that seem to be so commonplace today, namely, that Jesus never existed as a historical person, or that his virgin birth is copied from pagan deities etc. Again, apologetics is needed to answer those charges.