Why did Mendel face difficulties in explaining linked traits?

In a certain plant, red flowers $(R)$ are dominant to white flowers $(r)$ and tallness $(T)$ is dominant to dwarfness $(t)$. $A$ heterozygous plant $(RrTt)$ is backcrossed with a double recessive plant $(rrtt)$. If the gene loci for colour and size are situated very close together on the same chromosome, the expected percentage of offspring could be approximately:

Tall Red

Tall White

Dwarf Red

Dwarf White

respectively.

$A$: Crossing over is the exchange of genetic material between non-homologous chromosomes.
$R$: It produces new linkages.

Genes $A$ and $B$ are linked. What will be the genotype of the offspring produced by a cross between $AB/ab$ and $ab/ab$?

Which one of the following pairs is correctly matched?

In a test cross of a dihybrid plant with incomplete linkage,how many types of plants will be produced?