For a million and one individual reasons there are countless men with zero interest in the clothes on their back who leave the chore of buying their clothes to the women in their lives. I'd like to pawn off the job myself at times, but haven't a taker.
The real job becomes the thankless task of getting your guy to look presentable when he leaves home. It's never easy to dress someone who doesn't care, but several tips may work wonders.
Fit is everything, so stop buying dress clothes labeled Small, Medium, Large... Men's shirts are sold in sizes. The numbers (ie 16, 32) represent neck size and sleeve length. Get a tape and measure. Shirts that fit look better and feel better. Real honest to goodness identifiable fabric wears better and lasts longer than plastic. Silently, he'll thank you.
Many men deep into middle age believe they wear the same size pants as they did in high school. It ain't so. Nothing looks worse than dun lop (my belly dun lopped over my belt). Pants are sold even number waist and length, with the expectation that they'll hang from his navel. If he is between sizes go up, and have the waist altered. Tell him he looks thinner with pants that fit. If need be, your dry cleaner can size pants to fit. Once you get the waist size right, you'll only need to do this once.
Most guys who don't care what they wear live in khaki's and blue jeans, which can be fine, and getting them to try something new is always a fight. May I suggest that if you're looking for ways to expand his sartorial horizons, skip the fashion departments of the mall stores and search Google images. You could do worse than to emulate the look of two men with bags of money, professional stylist on call to dress them, access to everything, yet dress pretty squarely and always look great.
Prince Charles may be the best dressed man on the planet. His day to day wardrobe is probably fairly small, considering all the business and professional engagements he has. He keeps clothing until it can be mended no further, yet always looks sharp, even in khaki's and blue jeans. It may be that his people are acquainted with irons, but he is a walking clothing tutorial, and his look can be copied on a modest budget. Once again, proper fit is everything.
Ralph Lauren is in the fashion business, but it rarely shows. Much of his clothing has been hanging in his closet a long time. He dresses conservatively yet most always looks well put together. Again, his look can be copied over and over.
While I offer no guarantees, I do recognize that most men are vain. A few turns around the office in clothes made of identifiable fabric, that fit well will garner compliments, which may lead to his taking a bit more pride in his appearance.
Shoes we'll tackle some other day.