Why has Kurita not developed a new OmniMech, in fact?
*Points to smoking, radioactive crater that was one known as Luthien Armour Works.*
So to put things into perspective:
IS OmniMech Timeline:
3052: Battle fo Luthien, Draconis Combine receives a lot of Clan OmniMech salvage.
3052: Raptor (25t).
3054: Sunder (90t).
3056: Owens (35t), Firestarter-O (45t).
3057: Strider (40t).
3058: Black Hawk-KU (60t), BlackJack-O (50t), Perseus (75t).
3059: Avatar (70t), Arctic Fox (30t).
3060: Men Shen (55t), Hauptmann (95t).
3062: Templar (85t).
3065: Battle Cobra (C*-made, 40t).
3067/3068: Wobbie Jihad begins, LAW nuked.
3069: Malak (30t), Preta (45t), Grigori (60t), Deva (70t), Seraph (85t), Archangel (100t).
OmniMech tonnages: 25t, 30t, 35t, 40t, 45t, 50t, 55t, 60t, 70t, 75t, 85t, 90t, 95t, 100t.
Missing tonnages: 10t, 15t, 20t, 65t, 80t.
So yeah, not much time to R&D new omnimechs using new technologies since the last 2nd generation IS Omni (C* Battle Cobra). The Compact FE is from 3068, LFE from 3062 (Templar could've had it, theoretically), XXLFE simply cost too much. Compact Gyro is from 3068, Heavy-Duty Gyro from 3067, XL Gyro from 3067. Small CPit is from 3067, Torso-Mounted is from 3053 (this one might actually be useful). Endo-Composite is from 3067, Composite and Reinforced don't have crits so I can't check with SSW... TSM has limited use. Void-Sig is from 3070. Light FF is from 3067, Heavy FF from 3069, Stealth from 3063, Glazer/Reactive are from 3058/3063, not sure about Hardened...
So theoretically, if the Jihad hadn't happened, we probably would've seen 3rd generation IS omnis by now (other than the celestials). The biggest IS Omni factory lies in radioactive ruins, so that'll slow the process even further.
now ask yourself this. how long exactly did it take the Clans to develop their 2nd generation Omnimechs?
The Coyotl is from 2854, so it'd be about 16 years till the first 2nd generation Clan Omni (Nova). The IS did it even faster in only 6 years (Perseus is the first 2nd gen IS omni?). With the clans we see a couple of designs in the first half of the 2870s, then a gap until 2887 (13 year gap). Then a 3-year gap, a 10-year gap, a 26-year gap, 4-year gap, etc. So the IS is producing new Omni generations at a much higher rate.