The army has more volunteers for combat units than they have vacancies. People are turned away from combat units. This suggest that the army has no shortage of manpower. Given the proven importance of unit coehsion, the army doesn’t to wake up and discover that 20% of the soldiers are from an entirely different culture and share nothing in common with the rest of the unit.
However Israel is facing an existential threat. At current growth rates, the majority of the country will be Orthodox in the forseeable future. The whole zionist enterprise is based on the deal of converting Jews from backwards diaspora-oriented religious fanatics into good modern secularists (the “Am Hofshi” – free from the yoke of Torah – in their anthem).
In the past, a high percentage of soldiers became substantially less religious through army service, i.e., managed to adjust and become “normal”. While they don’t hope for the same sucess they had in getting most of the Sefardim to abandon backwards religious practices (they went from over 90% frum to less than 50%), with any luck enough hareidim can be normalized to keep Israel zionist rather than risk it turning Jewish. From their perspective, that’s a feature, not a bug.