Why are companies hiring and continuing new gras on OPT's rather than sponsoring H1?

[nisaga]

I have seen this new trend where companies are hiring fresh grads but asking them to continue on their OPT's (for 29 months when possible) even though there are still H1's available.

The two instances I've personally seen are
1) Tech company that sponsors around 50-100 H1B visas each year
2) Reputed academic institution for a post-doctoral position

Any insights on why this might be happening ?

Since intl. travel is generally discouraged on OPT, I can see at least one downside of this move for individuals.

[kabkaba]

It saves petition costs, hassle and it is less of a commitment for the employer if the employee does not require any sponsorship.
There is no such thing as travel discouraged while OPT. If you have valid Visa, proper job, EAD and I-20 with travel signature there is no problem in returning. Of course any time abroad is considered unemployed period and will be counted against the 90/120 day limit. However, if one has to apply for F1 Visa while on OPT that is risky.