Yes DPA's were put into law to avoid harming parties that aren't directly responsible for wrongdoing. However; you left out some conditions that qualifies a company for consideration of a DPA. Please note the term consideration. It isn't a guarantee that a DPA is offered even if the conditions are still met.
One big condition is "accept responsibility for, and stop, their wrongdoing". I have never once read anywhere in the media that SNC has accepted responsibility for their criminal acts. SNC has been doing dirty business for a while so it doesn't look like they were interested in stopping any wrongdoing. If their lobbying was effective to get the PMO to try to influence the AG to meddle in a criminal case when the prosecutors didn't offer them a DPA, please explain to me why SNC and the PMO shouldn't be facing obstruction of justice charges? I will help you a bit, jobs isn't anywhere near a good enough reason.
The PM and Liberals have been beating on the jobs, jobs, jobs, jobs, jobs and jobs drum. They quote 9000 jobs (the entirety of Canadian workers) will be lost and SNC will move out of Canada. Looking at SNC, they had a $15.2 billion backlog of work at the end of June 2018 (plus other contracts out) (
http://www.snclavalin.com/en/media/p...ults-2018.aspx). That work will have to be finished per contract demands which means people won't be losing their jobs outright tomorrow if SNC doesn't get a DPA. Furthermore, if SNC wants to move their business from Canada to another country, they would have to make a public announcement under the securities laws here in Canada in order to warn investors/future investors about potential losses to their stocks. So far all the news I have ever heard about an move was from the PM/Liberals saying SNC told him/them they may move. This is not a public announcement by the company so it is just smoke and mirrors by the federal government to try to defend what they did.
No one made SNC allegedly break the law. They allegedly did that on their own. If they are found guilty, they won't be starved of work, they will still be able to bid on private company contracts but not Canadian government ones. They have a very good minerals and metals division here in Toronto (I interviewed for a mechanical design job there a few years ago) whose main source of revenue is private contracts. The beating of the jobs drum doesn't fly well because there is no truth to it.
Will some jobs be affected? Sure. Will every person employed by SNC be issued a pink slip if a DPA isn't offered? No. Even if everyone lost their job tomorrow because of this, they would find work because they are very skilled individuals. Direct action by a government to save jobs isn't a door we want to open. I recognize Harper did it with the auto sector even though the direct action was supposed to be structured as a loan. I don't think the government should have given a red cent to the auto industry but my explanation would pull the thread off-topic.