Coach Johan Ackermann on Monday named his squad for the tour and opted for Springbok Elton Jantjies and Jaco van der Walt as his two flyhalves.
Boshoff, who played one Test for the Springboks against Scotland in 2014, will drop down to the Golden Lions’ Currie Cup squad.
“When I read that Marnitz was not included I immediately went and thought why he wouldn’t be picked. And I still can’t come up with a good reason why,” Van Straaten told Netwerk24.
Boshoff is seen as less of an attacking player than some of his team-mates at the back, but Van Straaten would still have included him in the Lions squad.
“Marnitz may not be a player that captures the imagination, but his distribution is effective and we know how reliable his boot is.
“We saw last season that he doesn’t just disappear in the Lions’ playing pattern. At times, he is the mainstay of it.
“Marnitz is the best kicker in the Lions team and he is good at varying his game. It was said that Jaco van der Walt was picked ahead of Marnitz because he can play several positions. Marnitz has played fullback before, so you can’t see he isn’t versatile."
The Lions kick off their campaign in Tokyo on Saturday, February 27 (06:15 SA time) against the Sunwolves which will be followed by matches against the Chiefs (March 5, Hamilton) and Highlanders (March 12, Dunedin).
The team departed for Japan on Tuesday.
Lions touring squad in alphabetical order:
Ruan Ackermann, Fabian Booysen, Andries Coetzee, Robbie Coetzee, Ruan Combrinck, Faf de Klerk, Ruan Dreyer, Andries Ferreira, Corne Fourie, Rohan Janse van Rensburg, Elton Jantjies, Jaco Kriel, Robert Kruger, Lionel Mapoe, Malcolm Marx, Howard Mnisi, Franco Mostert, Julian Redelinghuys, Courtnall Skosan, Dillon Smit, Dylan Smith, Warwick Tecklenburg, Armand van der Merwe, Jaco van der Walt, Jacques van Rooyen, Harold Vorster, Warren Whiteley (captain)