How do you motivate a conscript? When I was in the British Army, which is volunteer only, commanding a basic training troop if someone was wanted to give up we could say to them 'if this isn't for you then you can go home' (of course we did coach and mentor people to help them, I mean in cases where people just give up and stop soldiering when an exercise gets tough). They usually worked extremely hard to get into th…
Once someone is in the system, they can of course be flake out, but the routine and schedule both limit just how unmotivated individuals can be. In Norway, if you're a contrarian and refuse to do push-ups along with everyone else, eventually they'll send you home. That happens all the time, and I don't think it's a problem for the military: After all, they can just grab more people from the pool of candidates. But most people, once they're in the system, just don't dare to rebel.
There are countries, like Israel, which do make compulsory service work. My own experience in Norway was that the service was not executed seriously or even competently. Kids entered in with zero belief that war was ever likely to occur, and the attitude was that if it did occur, they were not going to play a meaningful part. This attitude was entirely validated by the ridiculously half-assedness of the training itself.
Generally, the basic training was more like a taster than real training. I was taught to fire a gun, but I probably fired 30 shots in total, and didn't feel I got good at it or comfortable wielding a gun. I was taught to throw a live hand grenade — one throw. Presumably they wanted to save on materiel. At one point, we were to do a rather exciting two-day war simulation in the woods, but around midnight, just as we were getting to the "dig a trench and watch for enemy patrols" stage, some colonel stepped in and shouted that we should all pack up because a lot of people were leaving for the Christmas holiday the next morning.
Also, the way compulsory service worked in Norway, you had one month of basic training, followed by 11 months of being stationed at some base. If you're, say, an army engineer, you might have some useful experiences, but for most people, it's just sitting around doing very little, and learning nothing. The real jobs are done by career professionals.
Long story short: If you want a good army you have to train them well, not treat them with kid gloves. Norway's system lead to a situation where a lot of young kids were given a small, not very serious look at military life, after which they'd go home and promptly forget everything. (Not that I'd have appreciated harder training at the time; I really didn't want to be there.) Part of fixing that would be to invest in recruits, just like you do with a regular army: Better materiel, more simulations, more specialization, and so on.
That still leaves the problem of what you do when people go back to real life. Norway's solution was to recall part of the population for a one-week "repetition" exercise every decade or so, which of course was just as silly and half-assed as the original endeavour.