This is not true. Monks in 5E have the same hps as Rogues and are 1hp behind fighters per level.
In 1e they were behind Fighters at every level and behind Rogues at every level after 1st. Even with a 16 constitution, when a Monk has the 2500xp to make level 2 the Rogue with a 16 con is at level 3 and is 3hps ahead of the Monk. He gets further ahead at every level after that. By the time the Monk has the 3.2M xp to make 17th level the thief is 24th level. That assumes the Monk won every single challenge or else the thief would be even further ahead and the monk has to stop there and even defend his position to avoid dropping to 16th level. The thief keeps going up and up.
Monks started with 2d4 for a maximum of 8 HP. Rogues started with 1d6 or 6 HP in 1e. Monks started ahead of Rogues in regards to HP base.
At level 2 the Monk has a base of 12 HP available, as does the Rogue, though with the more even scale of the 2d4 vs. 1d6 (or 3d4 at 2nd level vs 2d6 of a Rogue) the average for the Monk's HP is still higher than the Rogues base HP.
Monks fell behind a bit during mid levels but then did not STOP gaining HD at name level like other classes. Instead, they continue to get HD every single level.
In comparisons, Monks start with less HP in relation to other classes proportionally (they had two times the HP of Wizards, and more than Thieves and Assassins in 1e when created as a base, now though they have more HP than Wizards it is only by 2/3s and as you state, start with the same HP as a Rogue) and a lower maximum HP overall...which I pointed out originally.
If we REALLY want to get into the bushes, Monks also get a lower AC, lower damage and a whole slew of other nerfs. This probably originated in 3e where they nerfed the Monk pretty hard (and as I said, most likely due to racism, though probably not intentional racism on their part) and these nerfs have continued onwards into 5e, making it so that the Asian inspired class cannot be a toe to toe fighter or warrior, much less deal damage on the scale of others in many instances.
Why they feel the Monk cannot have as nice of things as other classes...well...institutional racism is a hard thing to overcome.
In some ways it originated with a racial bias (inspired by Kung-Fu the series and other movies, so based on those, but on a more awed inspired way, even if they didn't give the Monk ALL the nice toys it should have had even at the beginning) and that racial bias has continued, but gotten stronger in the way they view it so that the Monk got even LESS nice things than it did before.