One of the main focuses of Modern Family is the Dunphy family. Each of them is very different, especially the two daughters, Haley and Alex. Alex is the academic, intellectually gifted one who is constantly thinking about school, college, her career path — whatever stage in her life she might be at. Haley has never been school-oriented and is instead more focused on her social and love life, determined to have fun with more of a, "you only live once!" attitude.
Although these two have their soft, sentimental moments, there are many reasons the two of them weren't always close.
Alex Demeans Haley
Alex tends to be very demeaning about Haley and her intelligence. Whenever Haley doesn't understand a larger word Alex has used, she's impatient, and her jokes about what she perceives to be Haley's stupidity go over Haley's head. She occasionally expresses regret about being so mean towards her older sister, but it doesn't stop her doing it — the jokes about intelligence seem to have become impulse at this point, and can often cross the line from being funny into just plain nasty.
Haley Puts Alex Into Situations She's Uncomfortable With
Haley isn't a saint in their relationship though. She'll push Alex out of her comfort zone, but often to an unhealthy point — forcing her to chase boys when that's not what she wants to focus on, pushing her into makeovers with heels that she can't walk in and taking away her glasses so that she can't see. Haley sees this as what's best for Alex, but Alex literally injured herself doing one of these makeovers because her vision was impaired.
She Often Insults Her Appearance
She's quick to insult Alex's appearance and clothing choices. Alex doesn't wear as much make-up or Haley, or spend as much time obsessing over how she looks, which draws a lot of insults from Haley. She comments that the clothes Alex wears won't attract boys in her life, as if that's what Alex is aiming for even though she's said many times that's not what she cares about.
Haley Is Often Very Insensitive
Alex may not be the most sensitive person in the world, but Haley is somehow worse at times.
It's not just towards Alex. It's towards Andy, Dylan, anyone else in her life — even her parents. Her comments can be extremely cutting, and come with an air of only caring about herself. There are times Alex seems to be very much resent the way Haley treats not only her, but other people in her life.
They Have No Activities They Mutually Enjoy
It's hard to bond when you have nothing in common, and this is sadly the case for these two influencers. Haley's interests have always included make-up, blogging, social influencing — though those may expand now that she's a mother — but Alex's hobbies are what she would consider to be much more intellectual. Although they have attempted to bond together, it never lasts.
Haley Has Stolen From Alex
There are brief mentions of Haley stealing Alex's laptop to get through community college and copying her, as well as taking her clothes without permission.
Although Alex brings this up with Claire, she's only told that "sisters should share" and Haley gets away with it without asking for permission. This has probably caused a lot of resentment between the two, especially as Alex can't seem to rely on her parents to step in when boundaries are being pushed. And isn't that what parents are supposed to be for?
They Can't Understand Each Other's Priorities
Even though they don't share interests of priorities, they should be able to look at the other and understand why they're into the activities they are. Sadly, this isn't really the case.
Alex doesn't make an attempt to understand why Haley cares so much about her appearance or regards it as her whole worth, and Haley is too busy making fun of Alex's studious nature to understand how she wants to get far in life.
They Can Both Be Very Selfish
They have a tendency to be very selfish. Haley doesn't care about what's affecting Alex in particular — there's one episode where Alex is clearly very sick, and Haley drives her back to college and encourages her to stay there instead of where her family can take care of her. It's because Haley doesn't want Alex to realize she was fired, but there's little excuse for being that selfish.
They Don't Communicate
Perhaps these differences could be resolved if they actually talked — but they don't.
Instead, they snipe at each other, because that's how they're used to talking to each other. If they actually had a conversation about their differences, they might be able to mend a pretty damaged relationship.
They Were Cooped Up Together Too Long
In one episode, Haley expresses concern that when Alex moves out, she'll never talk to Haley. Alex claims she'll talk to Haley more when they aren't living together.
There's some wisdom to that. Alex seems self-aware enough to know that she and Haley don't always get along because they lived in the same house, and their family is so close and always forcing time together. They could never get a break from each other, which surely didn't help their relationship.