At 14 con (which is a reasonable to high con for a caster), there's a 35% chance to fail this check. Even with advantage (e.g. war caster), there's about a 12% chance.
If your DM consistently sends casters with higher con saves, he just really doesn't want you to ever break it.
And that's coming from someone that has a cloud giant wizard with a +10 con saves as the BBEG last session.
I think I'd build my caster's to have low enough Constitutions that they probably would have a 50/50 or similar. If someone is focusing on attacking the caster, I want to reward them by making the chance to end the concentration high.
Besides, for most games I've played, I recon right up into tier 3, most damage still comes in at under 20 per attack, so it's still a DC 10 save.