For years now, the masses have decried the downfall of control decks, especially in Modern. While it's true that they haven't been nearly as good as they were in the early days of Magic, and they have suffered in Modern in particular, control decks are still around in significant numbers. The people really love playing control decks.
I think the reasons for this are two-fold. First, players like playing lots of answers because they don't want to feel unprepared for any powerful threats from their opponent. It's a helpless feeling when your opponent casts a card that you can't answer, so you're left to sit there and watch it kill you. Control decks have theoretical answers to any potential threat through discard spells or counterspells and can answer other things on curve with removal, especially sweepers. You may not always have the right answer at the right time, but you're never sitting down hoping your opponent isn't playing a specific card you can't beat.
Second, players like having big, powerful effects. Lower-curve decks tend to be underpowered by the nature of the mana system in Magic, but a control deck that plays toward a long game can have a splashy win condition that is immensely satisfying to cast. If you haven't been around for too long, you may not remember Cruel Ultimatum, but few cards fit that bill more completely.
It generates a significant advantage at all three levels of the game: the battlefield, the hand, and the life totals. No matter where your opponent is trying to fight, Cruel Ultimatum will put a huge dent into their plans, and the combination of all three is often overwhelming.
In a game where you maintain parity until you cast it, the first copy is usually enough to end the game. But if you fall behind, you may need a second. Fortunately, in Modern, you have access to Snapcaster Mage, which becomes a second copy only two turns later, while the other cards you draw from Cruel Ultimatum hold the fort in the interim. The second copy is essentially unbeatable. Maybe someone has beaten it, but I would be skeptical.
Jeskai may be getting most of the press when it comes to control right now, but the metagame is reacting to Spell Queller and Fatal Push has proven its worth in the format. The ability to sideboard discard spells against combo decks is a huge boon as well. Grixis still gets a good creature-land in Creeping Tar Pit and the sideboard is well-rounded. I don't see why Death's Shadow needs to have all the fun when it comes to Grixis.