It all comes down to balancing positions. Or an attempt to.
I will try to keep it simple/short and please do not come at me with outliers. Upfront admissions, it does not fully balance the field. It just helps.
RBs carry the ball. WRs catch the ball. TEs block and hopefully catch.
In that basic overview, if everyone does their job, RB / WR score well as they are doing offensive related actions that matter in fantasy. TE is stuck doing line work and maybe catching some passes. This puts TE as not crucial to your team, on top of the fact you only typically start one of them. They are devalued in FF and often people punt that position.
Add in more points per reception and they become more interesting. In a 1PPR leauge, if TE gets a 1.5PPR you can take a TE who has 40 receptions but score like he had 60 (40 * 1.5). While the yards do not compound, that point bump makes TE more of an important piece to consider and you might find some sneaky values there. It helps account for some of their real world value blocking which has not FF value.
RBs carry the ball and especially now are catching lots of passes. WRs catch passes but rarely get carries. If you look at the above, the additional role of pass catching to positions that normally are not expected to is unbalancing. Just look at Jordan Howard and his value with no pass catching. Especially when you consider the RB aDOT is near or behind the line of scrimmage in many cases.
In this scenario which happens often a RB can catch a ball behind the line of scrimmage and get tackled, lose the team 3 yards but net a .7 (1pt for catch - .3 yards). They get an unnecessary point boost for just being near the QB catching unsuccessful dump offs. Even at .5PPR they net a .2 in the above scenario, but it lessens the act of catching what should be a very easy pass. They get full points for yards, just less for the catch.
WR catches the ball, and carries rarely. Even if they got a PPC point per carry they do not happen often enough to matter, but then the RB would also get a PPC and then things REALLY get out of alignment.
In the end, it is a way to account for player contributions per position, but not overly empower the RB while making the TE a bit more appealing. It makes it less easy to just punt the TE position. Certainly is not perfect, but it goes a step towards offering different roster constructs and potential trade values.
The real fun is the 2QB because then the QB definitely matters. Backups a regularly rostered and traded as actual currency where in single QB they are never even on rosters.
Does this help explain the reasoning?
Not that you asked, but here are my thoughts on scoring. I would strongly suggest the .5/1/1.5 or a .25/.75/1.25. In my mind the TE needs to be a full point over the RB, and unless the WR is at least double the RB there is too much value in RB.
Be sure to up the IDP as well or they will not be seen as much more than TE in standard leagues beyond the real top end players.