Does becoming more lax in Yiddishkeit make what someone is going through any easier? On the contrary, s/he should strengthen his/her commitment towards G-d, it will help him/her find meaning in the pain. For people who don't understand the purpose of this world, perhaps it's easy for them to leave Torah and mitzvos, because they can't understand why if G-d is good He is doing this to them. But for someone who is frum (by choice), recognizing that the here and now isn't the purpose of one's existence will be helpful in gaining perspective in what s/he is going through. However, it seems like it's quite the opposite. When someone goes through a hardship, sometimes it's a struggle to hold onto the fact that there is a G-d who loves him/her and is watching over him/her. And even when s/he does know that, it seems to be difficult to strengthen his/her resolve to be the best Jew s/he can be. Why is this the case?
I'm still trying to figure it out completely, but I'll share some of my thoughts. (They aren't all my own, some of them come from various friends whom I've discussed this topic with.)
Perhaps part of being single is not having to worry about how your actions will affect a family. You can be self-absorbed and do whatever it is you want without worrying that it may influence other people. If it's easier to sleep in and not daven by the zman, there isn't anyone who is going to take you to task for that or learn from your actions what is "okay" behavior. Things that start out innocuous can quickly become bad habits. While it's best to be doing things for yourself and your personal relationship with Hashem, sometimes the thing that keeps you in line is something else entirely. For example, you get excited about Shabbos, because you're teaching your young child about the beauty of Shabbos. Or, you watch what you bring into your house because you're looking out for the kedusha of your home, spouse, and family.
There is also the part where the person struggling is angry at G-d. S/he doesn't understand why s/he has to go through the tough situation, angry that G-d put him/her in these circumstances. Perhaps there's resentment too. "You're not giving me what I want, so why should I give You what You want?" Maybe s/he thinks, "I don't want to be close to You and do what You say I should, because it's not bringing me to a place where I can feel good about my life."
Additionally, like I've mentioned multiple times before, when things bring us pain, we disengage. If I can't be successful and feel productive as a member of frum society, because I can't be who I want here (married) and I don't feel like I fit in, I'm going to focus less on that and more on things that don't bring me pain. Thus, little things that perhaps I was more careful about before start falling through the cracks, because unfortunately they're no longer as important. My focus isn't the same. When you're trying to keep your head above water, the little gray areas don't end up mattering as much.
Another interesting idea why people become "less frum" as they go through challenges, is when people feel like they don't have control, they often flounder in this need for control. Take an anorexic for example. A lot of people that develop an eating disorder do so because there is something in their lives they cannot control, and this is an attempt to control something, anything. People who are going through a struggle flout rules and regulations as a means to gain more control in their lives, because they're wrestling with this need to control something.
Going through tough times is an opportunity for tremendous growth and strengthening one's relationship with G-d. That isn't always the easiest thing though, and sometimes it becomes about holding onto that relationship with Him even if you cannot be at the overall frumkeit level you were before.