Why is this the answer?

The answer is silk because this clever riddle is a special kind of word game that asks you to be a super detective and find four secret letters. To solve it, you must look carefully at the difference between two words in each line. Let's start with the first piece of the puzzle. The riddle says, "My first is in some but not in all." Think about all the letters in the word "some": S-O-M-E. Now, think about the letters in "all": A-L-L. Which letter is in the first word but not in the second? The letter 'S' is the key to the first part. Now for the second letter. The line is, "My second is in into but not in tall." Look closely at the letters in "into" and compare them to the letters in "tall." The special letter found in the first word, but not the second, is 'I'. So far, our mystery word is S-I. This is a common trick in riddles to make you pay close attention to which words share letters and which do not. Moving on to the third letter. The riddle guides us: "My third in little but no in big." The word "little" has many letters, but the one that makes it different from "big" is the letter 'L'. That gives us our third letter, and our word is growing to S-I-L. The fourth and final letter comes from, "My fourth in port but not in pig." When you compare "port" and "pig," the letter that is only in "port" is 'K'. When we put the four letters together, S-I-L-K, we get the word "silk"! This makes sense because the last part of the riddle tells us about the answer's use. It says, "My whole is made in nature's way. For clothing, rugs used every day." Silk is an amazing, shiny fabric that tiny silkworms help create in nature. People use this soft, beautiful material for making nice clothes like scarves and pajamas, and sometimes for decorating their homes with beautiful rugs. The riddle is solved by combining the secret letters and then thinking about what object fits all the descriptions, especially the final one about clothing and natural origin.